For Villains:
Bowser, Ganondorf, (technically) King Dedede, Bowser Jr. are already in game.
Ridley is an impossibility (so Sakurai says...)
King K. Rool and (technically) Wolf are front runners for the ballot.
That's pretty much all the big names right there. Bowser, Ganondorf, Ridley, K. Rool, Wolf, Dedede, and Bowser Jr. are all the most notable Nintendo villains. You have to get more obscure characters after that. The next biggest name I can think of is Porky from Mother/Earthbound and Medusa/Hades from Kid Icarus. Though it's possible to double dip into other franchises, there are no major contenders what so ever from series of the aforementioned villains (except maybe Magalor or Dark Matter from Kirby, both of which would actually BE a villain of that series, because Dedede is more of a heroic jerk than a villain). Ghirahim could also be a new contender for a Zelda rep, but he has some serious competition.
If we included 3rd party villains, the OBVIOUS choice would be Dr. Eggman. Though there is Dr. Wily, if we were to get another Megaman character it would be Zero without question. Dr. Eggman though feels like a shoo-in (aside from Tails and maybe Knuckles) if we got a second Sonic character. He's got as much clout as Bowser in the Video Game Villain department.
So yeah, maybe Porky and either Medusa OR Hades, not both obviously. Hades may have been the true final antagonist of KI: Uprising but Medusa has been in more games, and the final antagonist of the first KI, and she's a FEMALE villain, and Captain Syrup ain't happening ever (sadly) so Medusa has a lot more of an impressive resume than Hades, he merely has class.
I'd be all over Porky as playable but not so hot on anyone from KI. Fire Emblem falls into the same trap of having too many options with none being remotely more interesting than any other in their competition except for Black Knight, who at least warranted a Mii Costume. There's also Black Shadow to take Falcondorf's moveset so Ganon could get his own, which is literally all he has going for him.
Also keep it real, @
PushDustIn
glad to have you here for the time being. We'll be here, like we always are, until the fat kroc sings.