Bungie might not be willing to share any substantial details on their next, Activision-published project, but that doesn’t mean the gaming world will refrain from speculating about what the developer’s next massive game/franchise will end up being (My money is still on a total overhaul of Bungie’s first shooter series, Marathon).
Case in point: Bungie recently posted a job listing for a lead writer with experience creating “branching or non-linear” narratives. What does this mean exactly? Well, Gamespot seems to think it could suggest a possible action-RPG style along the lines of Mass Effect or Deus Ex.
Not a terrible guess given the “branching” specification; then again, Halo: ODST’s missions were technically non-linear, so it could just be Bungie plans to follow a similar mission structure for their post Halo: Reach title. Countering this though is another job listing for a player investment designer, whose job would entail developing a "robust and rewarding investment path, supported by consistent, rich and secure incentives that drives player behavior toward having fun and investing in their characters, and then validates those systems through intense simulation, testing and iteration." Hard to argue with the RPG-ishness of that.
Again, these are all just educated guesses at this point, so do with them what you will. Until we know more, why not toss out some thought bombs in the comments section?