Red Dead Revolution
It appears that there has been another "confirmation" (but this time in the UK) regarding the next title in Rockstar's RDR series.
As mentioned previously though, the game is not currently planned for existing consoles and was intended for next-gen consoles. Due to successful sales (6.9M), however, that certainly won't stop Rockstar from starting work on RDR3 right now.. after all, RDR2 (aka Red Dead Redemption) was originally developed for the PS2 & XBOX and then they updated the graphics and migrated it to the PS3/XBOX360. If the PS4/XBOX720 doesn't hit their release targets (2011-2012), Rockstar may just release RDR3 for existing consoles.. doubtful though.
You can definitely assume, however, that there will be a lot of DLC releases for RDR3 and the series. Most game developers have already jumped onto the DLC-bandwagon.. and others are joining (well, the greedy ones anyways). It's a great way to rush a game to retail, release half a game, and then release the rest of the game (incl. story endings and "closure") in small parts that you can charge money for. =]
Note: "Revolution" was actually a subtitle used for a demo video showing off RDR2 in-game content (fictional Mexican revolutionaries and missions). Although, the official RDR3 title could just as easily be changed to Revenge, Rebellion, Reckoning, Remembrance, Revelations, etc. etc.