Nope - they are two Lesser Evils, much like Andariel and Duriel, but we have not seen them yet... They are in conflict over who has higher control over Hell... At least for now...
Nope... Releasing that kind of new material would be another expansion to the game. Sure they'll add new runewords and stuff, but they can't just go in adding Belial and Azmodan and calling it good. Belial and Azmodan deserve their own time in the next installment.
I can't really believe that they would actually add new quests on a patch... That would be like a new expansion. It would sure be fun to see them do it though. I'd like to see them make quests that would lead up to the Diablo III sequel. It would be very exciting, but hightly unlikely.