At this stage, I'm just going to accept that Red Dead Redemption is never coming to PC, and cross my fingers that its sequel will (though there's no guarantee that will happen, either). As a lowly passive consumer of media products, bleak resignation is the sum total of the power I wield. But modders are different: if something doesn't exist, they can make it exist, as is evidenced by this effort to get Red Dead Redemption's map into GTA 5.
Red Dead Redemption 5 isn't promising the world just yet, but the mod is at least promising to bring the original game's map to GTA 5. While the GTAforums page doesn't allude to actual gameplay elements making the transition, third-party multiplayer clients like FiveMFiveReborn will be supported, meaning we may be able to shoot each other on the map, at least.
The modding team .White expects to release a beta in the summer (or winter in Australia). For those keen to partake in its development the team is "mostly looking for programmers who are able to help us reverse engineer the file formats" though help on mini-games and Dead Eye Targeting is also being sought.