Big Boss could stand a chance. Would be a good promotion for Ground Zeroes and manage to be a little bit different from SSBB. I recall Coles voice actor tweeting about working with David Hayter. So, makes sense to me.
Yu Narukami/Any P4 main character honestly. I'd love to see an AC rep, either Ezio or Connor. Lara Croft would be interesting, though I'm not sure what her moveset would be and how it'd be different from Drake's. Never played Disgaea but I'd like to see Laharl.