Yeh, I saw this trailor a few days ago on youtube. That is super sweet, you can be in multiplayer open world mode, and not play any of the games. You can just go around by yourself or with your posse and just do open-world stuff.
Revolutionary? Not quite. It's one heck of a step though. I wonder how many "lobbies" there will be? It's hard to imagine all the multiplayer players in a single open world, but then again, if it's big enough...
This game is going to be crazy good. Finally, the Old West genre has a benchmark game that could be a possible GOTY.