I'm thinking that it'll either be Bandana Dee, Skull Kid, Dixie, or a Pokemon revealed tomorrow. I don't really see an older character that a lot of casual fans might be unfamiliar with like Geno or Isaac being revealed in a general Direct, though it's certainly not impossible, especially since most of the people watching Nintendo Directs are more hardcore fans anyway.
That being said, I do think that a Pokemon is most likely for tomorrow, though I'm pretty indifferent to the idea of another Pokemon newcomer to be honest (Well, I guess Tapu Koko would be kinda cool). But a general Deerect is also what I figured would be a good place for Dee to be revealed, so I've got my fingers crossed.
Man... I wish this Direct didn't fall on a busy day for me. Hopefully when I'm done with my assignments I'll be greeted to some Dee-lightful news...