Yeah, if we did get a second Sonic character, it would be Tails, but I think a rep from a different SEGA franchise would make more sense since the leak depicts Ryu and not a second MegaMan rep.
Don't get me wrong, I wouldn't mind Tails, but I'm just not too optimistic about it.
I for one think it's not all that likely they choose a different Sega franchise character over a 2nd Sonic rep should Sega receive another character. There's no other Sega franchise that's as prominent on Nintendo consoles as Sonic. The only ones that even are a teensy bit are NiGHTS which had a Wii game (That wasn't very successful but one nonetheless) and to some extent Bayonetta although Sega doesn't actually have full rights to her as it turns out as
the only role Sega had with Bayonetta 2 was an advisory role. So Bayonetta doesn't quite count as a Sega rep. The only thing I could see is possibly some sort of ATLUS rep, but I wouldn't know a thing or to at all on who would be the most likely should Sega allow an ATLUS character to come in.
Ryu does have the excuse of being really prominent on Nintendo Consoles at one point and in fact his franchise put fighting games on the map in general. Sakurai himself was even a competitive Street Fighter player once.
I also think if anyone is added to Sega that isn't another Sonic rep. You'll have alot more "...Who?" messages. You don't want DLC characters you're adding to get the response of "...Who?"
I know you wouldn't mind seeing Tails, but you are kinda underestimating him as if he's a really obscure character. He's nearly, if not just as iconic of Video Game Sidekicks as Luigi and there would be plenty of Sonic fans who play Smash who would appreciate another rep. If Sega is to get another rep through DLC, I say Tails would be top billing.