Garteam
Smash Master
As far as base game DLC characters go, Ryu Hayabusa, Bomberman, Arale, and Marco Rossi seem to be in a good spot.
All four come from large franchises, have a ton of legacy behind them, and are accessible by virtue of being owned by Japanese companies that work with Nintendo. I think Ryu has the best chances due to being so popular during the Fighter's Pass era, but Bomberman actually getting an acknowledgement as an assist trophy and DLC Mii Costume suggests that Sakurai really respects the character.
All four come from large franchises, have a ton of legacy behind them, and are accessible by virtue of being owned by Japanese companies that work with Nintendo. I think Ryu has the best chances due to being so popular during the Fighter's Pass era, but Bomberman actually getting an acknowledgement as an assist trophy and DLC Mii Costume suggests that Sakurai really respects the character.