While we're about the business of speculation, what do we think about the prospect of xenos as potential classes? Kroot have already been laid out for RT, and there is precedent for them falling to Chaos. The main race I would personally be interested in is Dark Eldar. They would offer fairly high-level characters (given Chaos Marines may also be on the table) and would be a riot to play. The sort of toys they could employ (some of the best tech going) would also prove quite appealing...
But how the deuce do you persuade a disparate group to work together without backstabbing each other at every turn? Do you even attempt such a thing, given that's just what Chaos does? If you don't, though, won't games wind up being rather short-lived and confrontational?
So many questions at this early stage! I look forward to Design Diaries to help me figure out whether or not I am excited about this...
One thing that occurs re: xenos, the tagline of the game states '...the only price is your humanity.' Hmm! But could a Chaos Marine be argued to have had humanity to lose in the first place..?