Rockstar hasn't done it, so PC modders might as well.
It's pretty much what you'd expect: modders are taking Grand Theft Auto V and transforming it into the world of Red Dead Redemption. White Team is the outfit responsible for the creation, which they say will get a beta release come our winter and a teaser trailer fairly shortly.
The timing is pretty good, considering Red Dead Redemption 2 is due out in the autumn. According to the announcement, it's a "story mode modification" based off the Xbox 360 version of the game.
Weighing in at 2GB, RDRV will largely focus on "graphical improvements" - although as more modders put their hands up to help out, who knows where the mod will end. The team is currently looking for scripters to help recreate some of RDR's iconic features, like the slow-mo Dead Eye Targeting, and mini-games like poker.
You can stay in touch with the mod's progress over at the GTA Forums. There's zero chance the full thing will be finished by the time RDR2 comes out, but the beta will at least be out before RDR2 gets a PC port.