Paper Mario Toad/Captain Toad (and it would have to be the Captain considering Peach and Daisy still have regular Toad as a move) Geno Dixie Kong
I'd argue that those first two are probably above Waluigi. Paper Mario already has his own stage and Mario RPGs totally need representation. Geno would be a cool rep too, being a fan favorite and all, but Paper Mario is a long-running Nintendo series and Super Mario RPG is not.
Paper Mario maybe, but the others aren't as famous or popular.
And knowing Nintendo, a Paper Mario inclusion would have sticker and paint-based powers instead of being based on the good games.
Yeah, Waluigi should certainly be a priority over the last two but uhhhh, Toad has literally been in Mario since SMB 1! I'd say he's pretty famous. ---