if they add a SwoShld pokemon rep it would probably either be Scorbunny or Inteleon, the first being a mobile soccer player who kicks fireballs at people and the other is a lizard who channels his inner YuYuHakusho. Rillaboom is not so much a fighter as someone who makes awesome drumming montages for youtube.

For 3rd party? Crash, Doomguy, Dante, Master Chief, someone to rep Resident Evil (Jill Valentine or Chris Redfield?). Are all viable not-fightgame guys with some impact or recent exposure. Sora, and a much lesser extent the memepicks of Fortnite Jonesy, Gordon Freeman or Minecraft Steve have something they could possibly add.

Sub-Zero, Jin Kazama, Fulgore, Sol Badguy, or other fightgame reps might be interesting. Go crazy and bring out Blitztank as a playable, throw everyone for a bigger loop then when Piranha Plant was announced. Go indie and grab a Skullgirl, one of the Rivals of Ether characters, or someone from that "totally not a repurposed MLP fightgame" Fighting Herds.

Dig deep into the classic gaming vault and bring back Master Blaster, Frogger, a Battletoad...

or the gaming industry's "i guess everyone can use him?" longshot free-to-use nobody: The Baz.