From IGN's preview: http://xbox360.ign.com/articles/820/820752p3.html

quote:

New maps are pretty much a given, but given the nature of the game's design, we're not sure how likely it is that we'll see new roles or drivable vehicles added anytime soon.

I like how the achievements are pretty equally distributed between roles. Should help provide even more replay value to the game, not as if I won't be playing it a lot anyway. It is also nice, I can work on them, even when I have guest playing locally.