Bungie tease their next game might be a shooter type MMO or at least a new series that takes place over a set world/universe similar to World of Warcraft.
Only problem in the entire plan would be if the game come out for consoles, Bungie would need a separate studio to work on the PS3 version due to lack of experience and Activision might need to buy another studio since all their other studios are tied up in other game franchises.
http://kotaku.com/5657115/halo-creat...next-big-thing