No, I don't think he is, actually. He has a paint brush.
So there.
He also happens to be one of the main reasons why the Koopa Kids aren't seen as much, which almost instantly gains him a whole bunch of negative rep.
Bowser should just be the only Mario villian, as I can't think of any others which are truley deserving (That's you, Bowser Jr.), and the few I can think of who are deserving (Kamek), would simply make the Mario series even more over-repped.
King K. Rool has a large chance, and seeing as he was a trophey in Melee, it isn't like Sakurai doesn't know who he is. Besides, I think it's safe to say that Sakurai is looking to make sure that the DK series gets more representation, and other than Diddy Kong, K. Rool's the perfect choice.
King Dedede might as well already be comfirmed at this point due to the huge amount of support he has and the fact that he was supposed to be in the original but was scrapped due to time limits, than Melee, but was scrapped due to time limits again.
The villians in the Zelda series are much more memorable than most of the allies, which is why I'd support Skull Kid despite Gannondorf already being in the game.
Ridley also deserves to be in just because Metroid is so under-repped (I don't care what everyone keeps on saying; Zamus is nothing more than a transformation for Samus) and he'd also be incredably cool and original to play as.
Wolf would be neato, but I can't think of how to make him different from Fox. Obviously he could easily be unique, but I can't think of how they'd go about making him an individual.
The only thing stopping me from saying Dearthborn is the fact that 1. He's obscure and 2. He's only appeared in F-Zero GX. And I count Samurai Goroh as Falcon's rival, instead of a villian.