Granted, not all of the listed candidates are likely at the moment, but I thought I'd share anyways.
Alright, let's see. We got:
Dixie Kong, Toad, That Girl from Eternal Darkness, Mona, Magnus, Sylux, Goku, Rivali, ...Can't even make it out, Sukapon,
Karate Joe, Ray MK. III, Midna, dunno, still dunno, Baby Mario, Foreman Spike?, Hades, Pico, Tom Nook,
Gooey, King Hippo, That Guy from Ever Oasis, Jill, Cranky Kong, dunno, King Boo, Master Koga, Tsubasa Oribe,
Mipha, dunno, still dunno, really dunno, Doc Lewis, dunno, still dunno, Birdo, dunno, Ashley,
Chibi-Robo, Prince of Sable, Takamaru, That Guy from Sushi Strikers: Way of the Sushido, Viridi, Tetra, Dark Matter, Doshiin the Giant, dunno, Donkey Kong Jr.,
Samurai Goroh, Koopa Troopa, Skull Kid, Captain Syrup, Unnamed Girl from Rhythm Heaven, Ganon, Euden, Metroid, Andy, Marx,
Wario (Wario: Master of Disguise), Dillion, dunno, Kamek, Adeline, Black Shadow, Saki, dunno, Daruk, Elma
Mach Rider, Urbosa, Starfy, dunno, Isaac, Pom Pom, Porky, Bald Bull, dunno, Tiki,
Chozo, Yarn Yoshi, Rick & Kine & Koo, Uh...M-Mable? Marin?, Nikki, Seven, Medusa, Professor Wright (or something like that), Paper Mario, dunno,
K.K. Slider, dunno, still dunno, Sherrif, Krystal, Funky Kong, That Guy from Startropics, Captain Rainbow, Kumatora, and Tingle
81/100 ain't bad.
Anyway, a bit like what was said earlier, Nintendo doesn't have a shortage of cool characters, but it is running out of characters with high broad appeal. Like, how many people would care if Pom Pom were added to the game? How many would even recognize Doshiin the Giant? I don't think they're all bad additions, but as far as big, marketable DLC picks go, pretty much all of them miss the mark.