Well, here's my grand list of who I think it could be, divided into categories
Character predictions
1. Nintendo Owned
Gen 8 Pokémon (see section 7 for picks)
BotW Zelda
BotW Champion(s)?
Dixie Kong
Bandanna Dee
Chibi-Robo
Paper Mario
Euden (Dragalia Lost)
Metal Mario [gotta have a wildcard]
2. Sega Owned
New Sonic character
-Eggman
-Tails
-Blaze
-Metal Sonic
Arle from Puyo puyo
SMT 5 Protagonist
3. Capcom Owned
Phoenix Wright
Chun-li
Ametasteru
4. New 3rd Party (Japan)
Ryu Hiabusa (Koei Temco)
Granblue character (Cygames)
Reimu (Whoever owns Touhou)
5. New 3rd Party (misc.)
Rayman (Rayman, Ubisoft)
Crash Bandicoot (Crash Bandicoot, Lawsuit Magnet)
LoL character (League of Legends, Riot)
The Default guy from the game that all the kiddi-winks love. (Dabbing Simulator, Epic Lawsuit)
6. Stange grey area
Sora (Kingdom Hearts, Square Enix/Disney, What does the rodent have to say?)
Doomguy (DOOM, ID/Bethesda/Microsoft, Was negotiation had before the buyout?)
7. Pokémon Corner
Rillaboom
Cinderace
Intelleon
Haternne
Falinks
Dracovish
Zacian
Zamamzenta