I must be the only one that thinks the Smash 4 roster is pretty much perfect, eh?
I really can't think of any character that I wanted and they didn't add him. Except Mewtwo but they managed to please me quite fast.
I'm somewhat indifferent for Rayman, but it's probably the best choice as far as 3rd party goes. Bayonetta is worse than Snake and pretty much any other character is too niche and weird. The only other character I'd be fine with DLC is that red guy from TW101, but I don't really care about him that much.