It's Earthbound. You can never have over-representation.
I'm joking. Sort of. Anyway if they were to have another character I guess Pokey/Porky would be the most likely. I would assume he would be in the spider mech from Earthbound and he would be a heavy character. I just want another character that has different moves from Ness and Lucas, so Ninten wouldn't be as much fun but I hope they at least have alternate costumes(like wario) for some of the characters so you could have Ninten for Ness.
Maybe Giygas can be a character. He'd take up the whole stage. That'd be fun.