Since Nintendo selected the DLC, these are potential choices I think they could have gone with. Basically a mix of fan favorites, guests from franchises that have appeared on Switch and characters from recent/upcoming games they can promote.
Banjo-Kazooie (Banjo-Kazooie)
Byleth or Edelgard (Fire Emblem: Three Houses)
Crash Bandicoot (Crash Bandicoot)
Doom Slayer (DOOM)
Erdrick or Slime (Dragon Quest)
Geno (Super Mario RPG)
Monster Hunter (Monster Hunter)
Pokemon from Gen 8 (Pokemon 2019)
Rayman (Rayman)
Rex & Pyra (Xenoblade Chronicles 2)
Steve (Minecraft)
Waluigi (Super Mario)
Crash Bandicoot, DOOM, Dragon Quest, Minecraft, Monster Hunter and Rayman are all third party franchises that are major on Switch.
Banjo-Kazooie, Geno and Waluigi are fan favorites, the last of which has been acknowledged by Nintendo.
Fire Emblem: Three Houses, Pokemon 2019 and Xenoblade Chronicles 2 are all recent or upcoming games that can be promoted.
What do you guys think?