Last DLC was mostly third parties, so I'm hoping this one will be more Nintendo focused.
Paper Mario, Geno (really want Mallow but not happening), Melia, Isaac, Dixie Kong would be my top choices. I do recognize though that most of those won't really excite the masses.
I dont get the Geno hype. A side character that appeared half way through one game 25 years ago...
Well, he appeared pretty close to the beginning of the game. I believe you get him before the 2nd star you get out of seven. And the stars take (mostly) longer to get towards the end.
But there's the fact that it's an absolutely fantastic game that sadly hasn't gotten the love it should due to it being a collaboration. And Geno is also a sort of representative for the RPG style Mario games in general. Plus people are also hoping (probably foolishly) that they'll actually make a sequel, and that would be a sign. And, there really aren't a whole lot of other Nintendo characters to choose from anyway at this point, and if you'd prefer Nintendo to third parties, there aren't a lot of better options.