I understand your point but... Isn't that the same we can say about Captain Falcon, Fox McCloud, the Villager...?
To be honest, the most likely 3rd party character to me is Rayman. He had a recent love story with Nintendo, he already had a trophy in Smash 4, and even his awful spin-off had an X-Com crossover with Mario.
In regards to other contestants... Namco will have another rep if they still develop the franchise. Sega has two reps (
), so does Capcom (
), so I guess it is logical that we see a Namco rep (apart from
). I know that many would suggest Llody Irving or some character from either Soulcalibur or Tekken... but my bet is Solaire of Astoria.