All the roster needs for classic pre-2000 characters is Dixie and K. Rool and it'll be close to perfect.
For newer franchises Captain Toad (who technically counts as a new character), ARMS, and Xenoblade 2 are likely. Simon Belmont from Castlevania is also the heavily rumored third party character this game, and with Snake returning and Bomberman being an Assist trophy, it would make a lot of sense if Konami got a new rep.
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