Looks like we might be seeing a PC version for Red Dead Redemption 2 after all.

From a PC mention on a Rockstar employees' linkedin to a retailer posting a listing for the PC version of Red Dead Redemption 2, rumours have been flying around like crazy speculating that the game will have an appearance on Steam sooner or later.

However, the most concrete rumour so far has appeared - inside the files of the Red Dead Redemption 2 Companion App. That's right, the app itself has references to a PC version and multiple settings that would come with it! See for yourself!

Thank you to BlackScout for discovering this.

The most interesting parameters are so:
PARAM_FrameLimit - A framelimiter.
PARAM_DX11Use8BitTargets - Probably due to Xbox One.
PARAM_HDStreamingInFlight - Present in GTA V (PC)
PARAM_Oculus
PARAM_companionAutoConnectIpDurango  
PARAM_companionAutoConnectIpOrbis
PARAM_companionAutoConnectIpPC
PARAM_singleThreadedRenderer
PostFX::g_CheckerBoardEnable

Here is more evidence:
CommandIsPcVersion(void)    000000000166A12C

There may also be a PC version of the companion app:
SIGNIN_ANDROID_APP_URL    0000000002A866D0  
SIGNIN_IOS_APP_URL    0000000002A9C890  
SIGNIN_PC_APP_URL    0000000002A51F58

Here are the rest:

PARAM_ParticleCountScaleQuality
PARAM_ParticleLightingQuality
PARAM_ParticleOverallQuality
PARAM_ParticleShadowQuality
PARAM_UseDefaultResReflection
PARAM_WaterReflectionResX
PARAM_WaterReflectionResY
PARAM_anisotropicQualityLevel
PARAM_disableBokeh
PARAM_dx11shadowres
PARAM_enableHDR
PARAM_forceadpcm  - Oh no
PARAM_highColorPrecision
PARAM_noHDR
PARAM_reflectionBlur - New
PARAM_taa - New
PARAM_uiUseNewPauseMenu
PARAM_uiUseOldPauseMenu
PARAM_3rdPartyDir    0000000002DD2ED0
PARAM_ChallengesShowAll    0000000002F6C760
PARAM_DOFHighResEnabled    0000000002F9EB00
PARAM_DX11Use8BitTargets    0000000002BF4F1C
PARAM_FPSCam    0000000003043940
PARAM_FailNetworkTransition    0000000002BC7000
PARAM_ForcePresetMessageUpload    0000000002FB7750
PARAM_GoogleAnalyticsDebug    0000000002FB3408
PARAM_GoogleAnalyticsDisable    0000000002DCAA58
PARAM_HDStreamingInFlight    0000000002BE5480
PARAM_InputTouchVisualise    00000000030CD408
PARAM_MaxLODScale    0000000002C37608
PARAM_MaxPower    0000000002BE5088
PARAM_MinHeight    0000000002F68630
PARAM_MinPower    0000000002BF4B84
PARAM_MinWidth    0000000002FBA3A1
PARAM_MotionBlurStrength    0000000002FBDB48
PARAM_Oculus    0000000002F7FC10
PARAM_ParticleCountScaleQuality    0000000002FBA480
PARAM_ParticleLightingQuality    0000000003043370
PARAM_ParticleOverallQuality    0000000002DC6CD8
PARAM_ParticleShadowQuality    0000000002F832A8
PARAM_PreciseHit    0000000003048A30
PARAM_SCFeedForceOfflineTiles    0000000002FBDF20
PARAM_SCFeedHideDevTiles    0000000002FB3F80
PARAM_SSA    0000000002F68C38
PARAM_SSAO    0000000002F80790
PARAM_ScEnv    0000000002F6838C
PARAM_StartUpForceAllPlatformAvailable    0000000002F7EF40
PARAM_SuperMaxPower    0000000002FB94F0
PARAM_UseAutoSettings    000000000304A460
PARAM_UseDefaultResReflection    0000000002BC6CD4
PARAM_WaterReflectionResX    0000000002DDF748
PARAM_WaterReflectionResY    0000000002F96978
PARAM_allowExportPathLoads    0000000002BD1E70
PARAM_alwaysShowTheseAsserts    0000000002F9EA79
PARAM_anisotropicQualityLevel    0000000002BD0120
PARAM_artdir    000000000304A538
PARAM_askToBugAsserts    0000000002FB7AA0
PARAM_assertOnDeprecatedPromptUse    0000000002BC1B34
PARAM_assetsRoot    0000000002C38790
PARAM_assetsdir    0000000002DD0CD0
PARAM_audiopack    0000000002DD29D0
PARAM_audiopacklist    0000000002B9E548
PARAM_audiopatchpack    0000000002BE5C78
PARAM_autocreateCollectableWidgets    0000000002BC4C88
PARAM_autocreateCompendiumWidgets    0000000002F6C834
PARAM_autocreateGoalWidgets    0000000002C35DA0
PARAM_autocreateJournalWidgets    0000000002B899D8
PARAM_autocreateMissionWidgets    0000000002F6B0B0
PARAM_autocreateStatWidgets    0000000002FBC354
PARAM_breakonassertid    0000000002FBC9B0
PARAM_breakoncontext    0000000002FB7B98
PARAM_breakonname    00000000030C9000
PARAM_bucketstat    0000000002F9E980
PARAM_bugErrors    0000000002F82DD8
PARAM_bugIncludeContext    0000000002DD226C
PARAM_buildBranch    0000000002B99498
PARAM_buildRoot    0000000002BF0A40
PARAM_build_override    0000000002DE7C28
PARAM_canBugErrors    0000000002F7FDB8
PARAM_cashinventory_hostname    0000000002BD0040
PARAM_cashinventory_manifestid    0000000002BD1DB0
PARAM_cashinventory_nobundles    0000000002BC0A44
PARAM_cashinventory_noitemdatabasecache    0000000002BC4CA0
PARAM_cashinventory_notimeout    0000000002DE0C20
PARAM_cashinventory_showspamspew    0000000002BE51E8
PARAM_cashinventory_timeout    0000000002DF2758
PARAM_cashinventory_usegui    0000000003079BD8
PARAM_catchDataFile    0000000002BA1718
PARAM_cheapmode    0000000002DE0D18
PARAM_checkUnusedFiles    0000000002FBBFD8
PARAM_cityDensity    0000000002F83040
PARAM_cleaninstall    0000000002F80B48
PARAM_cloudAllowCheckMemberSpace    0000000002C37DFC
PARAM_cloudCacheAll    0000000002BF4AD8
PARAM_cloudCacheDisableEncryption    0000000002BE5BF0
PARAM_cloudCacheDisabled    0000000002C38AD8
PARAM_cloudCacheNone    0000000002DDF8B8
PARAM_cloudCachePackaged    0000000002B99230
PARAM_cloudForceAvailable    0000000002BCFFDC
PARAM_cloudForceEnglishUGC    0000000002BE62B0
PARAM_cloudForceGetCloud    00000000030CDD10
PARAM_cloudForceNotAvailable    0000000002F68888
PARAM_cloudForceUseCache    0000000002C35D88
PARAM_cloudNoAllocator    0000000002FB3698
PARAM_cloudUseStreamingForPost    0000000002BC0BB4
PARAM_cloudkey    0000000002DE0998
PARAM_codeBranch    0000000002F6C7B0
PARAM_common    0000000003050A58
PARAM_commonpack    0000000002FBC2E0
PARAM_companionAutoConnect    0000000002DD2124
PARAM_companionAutoConnectIpDurango    0000000002F68418
PARAM_companionAutoConnectIpOrbis    0000000002C38748
PARAM_companionAutoConnectIpPC    0000000002F985B8
PARAM_companionConnectionPort    00000000030CD4A9
PARAM_companionSkipInventoryDownload    0000000003053938
PARAM_companionappserver_connect    0000000002DCEB14
PARAM_compendiumHasAllEditions    0000000002BA2990
PARAM_compendiumUnlockAllItems    0000000002BE6434
PARAM_controlRemoteIP    00000000030CD880
PARAM_create_artifacts    000000000303E7D0
PARAM_debugMemstats    0000000002FBB0A4
PARAM_debugSafeframeMargin    000000000304325C
PARAM_debugUiObjectsPath    0000000002BC39CC
PARAM_debugpatch    0000000002FB74C0
PARAM_diagTerminateIgnoreDebugger    0000000002BE2BB8
PARAM_disableActionProxy    0000000002BD3130
PARAM_disableBokeh    0000000002F7EEC8
PARAM_disableStatObfuscation    0000000002BE45F8
PARAM_disable_all_plugin_tasks    0000000002B989C0
PARAM_displayDataFileType    0000000002DCF358
PARAM_dontForceImpersonation    0000000002BC3A40
PARAM_dumpItemdatabaseCollection    0000000002F98CE0
PARAM_dx11shadowres    00000000030438F8
PARAM_enableHDR    0000000002FBC420
PARAM_enableOverlappedIO    0000000002C37E8C
PARAM_eurobuild    0000000002C37371
PARAM_fileloader_ignore_packfile    000000000307A86C
PARAM_fileloader_tty_windows    0000000002B899BC
PARAM_fogVolumes    0000000002BE64D8
PARAM_forceLoadoutWeaponMgr    0000000002BC4BC8
PARAM_forceadpcm    0000000002F65C69
PARAM_fxaa    0000000002BD1838
PARAM_gameserver_protomode    0000000002BE9D71
PARAM_gameserver_unittest    0000000002DDFAD8
PARAM_genStatsMeta    0000000002F7E1D9
PARAM_geoLocCountry    0000000002DD07C8
PARAM_geoLocFakeIp    0000000002FBAC38
PARAM_grassQuality    0000000002F58340
PARAM_highColorPrecision    0000000002F57BD0
PARAM_httpNumThreads    00000000030CE1A0
PARAM_httpPort    00000000030CE35C
PARAM_httpThrottle    0000000002BE52F8
PARAM_ignoreDifferentVideoCard    0000000002B98680
PARAM_inventoryChangesCallstack    0000000002F979C8
PARAM_jpnbuild    00000000030CD4A8
PARAM_lan    0000000002BC0B04
PARAM_legacystatflushing    0000000002BD1D74
PARAM_level    0000000002BE4EE0
PARAM_loadDevOnlyData    0000000002F57D30
PARAM_loaddebugmanifest    0000000002BD1830
PARAM_loadgameservermeta    0000000002FB3B24
PARAM_loadpacksfrommanifest    0000000002F831B5
PARAM_loadstats    0000000002C38718
PARAM_lockscaleformtogameframe    0000000002DE0038
PARAM_lodScale    0000000002B6B7F8
PARAM_logAssertsToFile    0000000002B8FB98
PARAM_maponly    00000000030CE4D8
PARAM_maponlyextra    0000000003048990
PARAM_marketing    0000000002DCEA64
PARAM_measure    0000000002FBCA70
PARAM_memstats    0000000002F7FC60
PARAM_minigame_connect    0000000002BF09D8
PARAM_missingfilesarefatal    0000000002F82F90
PARAM_mode    0000000002BE8B48
PARAM_netCompliance    0000000002BC2030
PARAM_netConnectToGangMembers    0000000003043920
PARAM_netEnableFriendCrewTicker    0000000002DE02A8
PARAM_netNoCrewEmblems    0000000002FB3FE8
PARAM_netPrivilegesAgeRestricted    0000000003048E24
PARAM_netPrivilegesMultiplayer    0000000002DF2E60
PARAM_netPrivilegesRos    0000000002F65C68
PARAM_netPrivilegesSocialNetworkSharing    0000000002BE2AFC
PARAM_netPrivilegesTextCommunication    0000000002FB8C40
PARAM_netPrivilegesUserContent    0000000002BE8A20
PARAM_netPrivilegesVoiceCommunication    0000000002BA1660
PARAM_netProfanityAllowPlatformCheckFailure    0000000002DCF198
PARAM_netScPrivateSession    0000000002B9A950
PARAM_netScSeamlessPvE    0000000002BEA8AC
PARAM_netTelemetryConfig    00000000030799D4
PARAM_netTelemetryDump    0000000002BA0860
PARAM_netTelemetryDumpPath    0000000002B97BBC
PARAM_netTelemetryForceOff    0000000002BE62D0
PARAM_netTelemetryForceOn    0000000003053A08
PARAM_netTelemetryGroupForceOff    0000000002C387B8
PARAM_netTelemetryGroupForceOn    0000000002BE61D0
PARAM_netlogprefix    00000000030CD958
PARAM_noConnectionWait    0000000002F98D70
PARAM_noHDR    0000000002DE9688
PARAM_noInGameDOF    0000000002B8FD70
PARAM_noSCFeed    0000000002B98A48
PARAM_noactionscriptclassoverride    0000000002F65C80
PARAM_noaudio    0000000003079120
PARAM_nocheats    0000000002F688E4
PARAM_nodebugpack    0000000002F68394
PARAM_nographics    0000000002BC1E98
PARAM_nonetwork    0000000002BF0AA0
PARAM_nooutput    0000000002BA4178
PARAM_noscaleformmovie    0000000002DD2D98
PARAM_nostacktraceonasserts    0000000002B99860
PARAM_notimefix    0000000002B712D0
PARAM_notimeouts    0000000002BD1400
PARAM_nowebserver    0000000002BCFF99
PARAM_output    0000000002B89A18
PARAM_override_script    0000000002FBDDA0
PARAM_override_script_dlc    0000000002F82BDC
PARAM_parsercatalog    0000000002FB7D88
PARAM_particleQuality    0000000002DCEBA0
PARAM_particleShadows    0000000002BE6620
PARAM_pedLodBias    0000000002BC3918
PARAM_pedVariety    0000000002DE1588
PARAM_physicalreserveblockKB    0000000002DD3178
PARAM_platform    0000000002B97CB4
PARAM_platformpack    0000000002B9A7E8
PARAM_playgoemu    0000000002FB94E8
PARAM_playgotest    0000000002FB91C8
PARAM_postFX    0000000002F82F98
PARAM_postfxusesFP16    0000000002BD3170
PARAM_previewfolder    0000000002B98A2C
PARAM_privacyUpsellWaitTimeSec    0000000002FB3A38
PARAM_projRoot    0000000002F82EE8
PARAM_psoNoDebugStrings    0000000003048FFC
PARAM_qaAssertBugHelper    0000000002FBA2C0
PARAM_ragUseOwnWindow    0000000002F65A90
PARAM_rageDir    0000000002FB9ED0
PARAM_randomseed    0000000002BF0F9C
PARAM_reflectionBlur    0000000003043C78
PARAM_reflectionMSAA    0000000002DD2FA8
PARAM_reflectionQuality    0000000002BF54A0
PARAM_requireMetapedHolster    0000000002BC1FF8
PARAM_res    0000000002BF4A28
PARAM_rlPosixTimeDelta    0000000002BE8748
PARAM_rootdir    0000000003050A64
PARAM_rpcconnectiontester_usessl    0000000002F80850
PARAM_runscript    0000000002BF2D00
PARAM_safemode    0000000002BC3E08
PARAM_scFeedIdInTitle    0000000002BE65B0
PARAM_scFeedNumberInTitle    0000000002BF5548
PARAM_scFeedTypeInTitle    0000000002F9E8E0
PARAM_scaleformdebugfont    0000000002DCDE28
PARAM_scalingMode    0000000002BE9DF8
PARAM_scriptInstructionLimit    0000000002BE5890
PARAM_scriptProtectGlobals    0000000002BD30E4
PARAM_secondScreenGameListOnly    0000000002C35DF8
PARAM_secondScreenGames    0000000002B6D414
PARAM_shaderQuality    0000000002B6D608
PARAM_shadowAircraftWeight    0000000002BA09E0
PARAM_shadowDisableScreenSizeCheck    0000000002BA13E8
PARAM_shadowDistance    0000000002F167D8
PARAM_shadowLongShadows    0000000002FB76B0
PARAM_shadowQuality    0000000002BCF150
PARAM_shadowSoftness    0000000002BF4820
PARAM_shadowSplitZEnd    0000000002BE6288
PARAM_shadowSplitZStart    0000000002BF51C0
PARAM_sharpen    0000000002DCE890
PARAM_showAwardsImGui    0000000002BCFF44
PARAM_singleThreadedRenderer    0000000002BD2CB8
PARAM_slowLoad    0000000002BC6D20
PARAM_spactionproxy_connect    0000000002BF38EC
PARAM_stacktraceonerrors    0000000002BE99B8
PARAM_startupscript    0000000002BF54E8
PARAM_stealextramemory    0000000002BD3028
PARAM_taa    0000000002BCB0A8
PARAM_telemetrynodebug    0000000002F80AB0
PARAM_telemetryplaytest    0000000002F68C30
PARAM_tessellation    0000000002B989D8
PARAM_testintelligentdelivery    0000000002DD15C9
PARAM_textureQuality    00000000030CDCB0
PARAM_ticketExpirationSec    0000000002BC0D78
PARAM_timeout    0000000003053B20
PARAM_toolsRoot    0000000002F831B8
PARAM_trimChallengeSave    0000000002DD1818
PARAM_ttyframeprefix    0000000002DD315D
PARAM_tunableCloudFile    0000000002C38034
PARAM_tunableCloudNotEncrypted    0000000002F7F150
PARAM_tunableLoadLocal    0000000002F57B08
PARAM_tunableLocalFile    0000000002FBC184
PARAM_tunableMemberFile    0000000002FB94E9
PARAM_tunableNoWriteToFile    00000000030CDBF8
PARAM_tunableNoWriteToLogs    0000000002DCF6B0
PARAM_txaa    0000000002FB96D0
PARAM_uiUseNewPauseMenu    0000000002DD0A08
PARAM_uiUseOldPauseMenu    0000000002BC1B40
PARAM_ultraShadows    0000000002FB9498
PARAM_unlockWeapons    00000000030C8FF0
PARAM_unlockall    0000000002BE5180
PARAM_useContextBasedZoom    0000000002B976B8
PARAM_useMaximumSettings    0000000002C38788
PARAM_useMinimumSettings    0000000002F832D8
PARAM_useScriptLoadoutScreen    0000000002F7FB48
PARAM_useWeaponsPatch    0000000002F7F751
PARAM_usefatcuts    0000000002BE5E74
PARAM_usegameservicesauth    0000000002F832D4
PARAM_usepackedassets    0000000002BF0F78
PARAM_usepackfiles    0000000002DF2DE8
PARAM_userdir    0000000002F569F0
PARAM_usesocketpow    0000000002BC1C20
PARAM_validatescripts    0000000002BC1F8C
PARAM_vehicleLodBias    0000000002F80370
PARAM_vehicleVariety    0000000002DDFFB8
PARAM_verifycachedmovespeeds    0000000002BF2B9C
PARAM_virtualreserveblockKB    0000000002DCED40
PARAM_waterQuality    0000000002DE7CF8
PARAM_weaponMoveTransactions    0000000002C38230

Then some Advanced Graphics settings:
parser_rage__fwuiAdvancedGraphicsSettings_checkerboardEnabled    0000000002B669D8
parser_rage__fwuiAdvancedGraphicsSettings_cityDensity    0000000002B66640
parser_rage__fwuiAdvancedGraphicsSettings_dof    0000000002B66820
parser_rage__fwuiAdvancedGraphicsSettings_dofHighResEnabled    0000000002B66848
parser_rage__fwuiAdvancedGraphicsSettings_dxVersion    0000000002B66568
parser_rage__fwuiAdvancedGraphicsSettings_eAPI    0000000002B66B10
parser_rage__fwuiAdvancedGraphicsSettings_fxaaEnabled    0000000002B66938
parser_rage__fwuiAdvancedGraphicsSettings_hdStreamingInFlight    0000000002B66870
parser_rage__fwuiAdvancedGraphicsSettings_lightingFogVolumes    0000000002B66A28
parser_rage__fwuiAdvancedGraphicsSettings_maxLodScale    0000000002B666B8
parser_rage__fwuiAdvancedGraphicsSettings_maxTexUpgradesPerFrame    0000000002B667F8
parser_rage__fwuiAdvancedGraphicsSettings_motionBlurStrength    0000000002B666E0
parser_rage__fwuiAdvancedGraphicsSettings_particleCountScaleQuality    0000000002B66780
parser_rage__fwuiAdvancedGraphicsSettings_particleLightingQuality    0000000002B66730
parser_rage__fwuiAdvancedGraphicsSettings_particleOverallQuality    0000000002B66708
parser_rage__fwuiAdvancedGraphicsSettings_particleShadowQuality    0000000002B66758
parser_rage__fwuiAdvancedGraphicsSettings_pedVarietyMultiplier    0000000002B66668
parser_rage__fwuiAdvancedGraphicsSettings_postFX    0000000002B66530
parser_rage__fwuiAdvancedGraphicsSettings_reflectionMipBlur    0000000002B668E8
parser_rage__fwuiAdvancedGraphicsSettings_scatteringVolumeQuality    0000000002B66AA0
parser_rage__fwuiAdvancedGraphicsSettings_shaderSSA    0000000002B66A50
parser_rage__fwuiAdvancedGraphicsSettings_shadowAircraftExpWeight    0000000002B66618
parser_rage__fwuiAdvancedGraphicsSettings_shadowDisableScreenSizeCheck    0000000002B66910
parser_rage__fwuiAdvancedGraphicsSettings_shadowDistance    0000000002B665A0
parser_rage__fwuiAdvancedGraphicsSettings_shadowLongShadows    0000000002B66A78
parser_rage__fwuiAdvancedGraphicsSettings_shadowParticleShadows    0000000002B668C0
parser_rage__fwuiAdvancedGraphicsSettings_shadowSoftShadows    0000000002B664F8
parser_rage__fwuiAdvancedGraphicsSettings_shadowSplitZEnd    0000000002B665F0
parser_rage__fwuiAdvancedGraphicsSettings_shadowSplitZStart    0000000002B665C8
parser_rage__fwuiAdvancedGraphicsSettings_sharpenEnabled    0000000002B669B0
parser_rage__fwuiAdvancedGraphicsSettings_taaEnabled    0000000002B66988
parser_rage__fwuiAdvancedGraphicsSettings_txaaEnabled    0000000002B66960
parser_rage__fwuiAdvancedGraphicsSettings_ultraShadowsEnabled    0000000002B66898
parser_rage__fwuiAdvancedGraphicsSettings_vehicleVarietyMultiplier    0000000002B66690
parser_rage__fwuiAdvancedGraphicsSettings_velocityBufferEnabled    0000000002B66A00
parser_rage__fwuiAdvancedGraphicsSettings_volumetricsQuality    0000000002B66AD8
parser_rage__fwuiAdvancedGraphicsSettings_waterReflectionResX    0000000002B667A8
parser_rage__fwuiAdvancedGraphicsSettings_waterReflectionResY    0000000002B667D0