Of course I'd support a bearded Isaac because Smash needs more fighters with beards. We already have enough mustaches!
Also, they should add this guy because he looks like Wolverine (without claws):
In all seriousness, there's a lot of obscure/lesser-known games, however in Brawl we did get some content (mostly multiple stickers or trophies) from lesser-known series (including Japan-only). Not all, of course, but a good amount. And there's some Nintendo published games that didn't do so hot in sales (mostly talking Wii games), but I'd love to see some content from them. Yeah, I have a character in mind, but it ain't gonna happen, unless if they are seriously hoping to green-lit another game by testing such character in Smash for popularity and whatnot, kinda like Pit's revival in Brawl.