I agree with Alex2247, the Mafia theme is getting old (even though we only had it in GTA3 and LCS, VC wasn't really Mafia that much, just a touch of it which is what made it so good) and we've tried gangbanging which not a lot of people liked and now maybe a Latino/Hispanic theme would be pretty cool.
VCS isn't really going to have a real kind of theme now that I think about it. Since your not in a gang but your a drug dealer/marine (or ex-marine I don't know) and I think it's going to be a lot like Vice City where you do missions for a lot of different people: different gangs, clients, or maybe crooked cops, etc.