I haven't seen this discussed, and it seems like a long shot, but I actually think that Ryu from the "Breath of Fire" series could work well.
They did say there was a possibility of Capcom characters (not too many, and I expect MegaMan) and the first two were on SNES and GBA (and I think the virtual console).
You could have him in his normal form (I would think a mix of Marth and Link), and he could change to dragon form (like Charizard), and his Final Smash could be his Agni form or something.
Of course this seems like a long shot. 3-5 were on Sony systems and the most recent was released a decade ago, but the people gunning for him to be in MvC have been consistently disappointed, so I feel like he could still be available for SSB4. He could be like the completely unexpected character, like R.O.B. in Brawl.
Any thoughts on this?