To me, it's obvious that there's a big gap and a bigger demand for villains (playable and otherwise). As far as heroes go, there seems to be a lot more fertile ground to add
characters to the game from the X-Men side of the marvel universe. Magik being added is very exciting and I would
hope that we might see more New Mutants or X-Force related characters....
Warlock (w/ Cypher as support)
Non X-men Heroes (a lot harder to come up with good ones that we don't already have):