I'd REALLY want to see Jill but it won't happen. As for characters, I think its clear that only plot important character would hit SSB4; personally, Krom would be the first choice since he's the star of FE13 (maybe tied with him is you know who).
Mmmm, seeing as Ganondorf and Bowser appeared in Melee (as well as Mewtwo who is not entirely a villain), then Wario and King DDD (who once again, I don't see as a villain), I hope they would include one. They have many options with this one (Black Knight, Zephiel, Gharnef, FE13 enemy cast), then the Smash cast needs more villains too.