Toad, Dr. Mario (as a seperate character,) Waluigi, Mii, Samurai Goroh and Toon Link are the ones I don't want in the game.
Toon Link's spot seems secured, so that's already a lost cause.
Samurai Goroh just seems like a waste of character, his moveset would have to be completely made up, and he'd just steal the spot from a more deserving character. Would more or less be a forced F-Zero rep.
Mii just sounds lame, especially considering that no matter what you Mii looks like it'd have to be the same moveset, unlike in Mario Kart Wii where there was size differences.
Waluigi is just a stupid character in himself... I wouldn't mind him as much as the other characters though, at least he'd be fun to beat up and make "Too bad, Waluigi Time" jokes with.
Dr. Mario is as cloney as it gets, keep him away please. At most make him an alt skin for Mario, should be possible to make his fireballs into pills today.
Toad is the worst though. I don't like Toad in the Mario games, he doesn't have any good moveset potential, he isn't a fighter, and even in the NSMB games he's just the character that the people who are late to the party get to play.
Worst part is that all of these at least have a chance to get in the game, with Mii probably having the least chance.
Add in every 3rd party except for Mega Man on there and that's about it, though I don't believe any 3rd parties besides him has a chance.