Speaking of Mii costumes, what characters would you like to see as a "premium" Mii costume? (no obvious troll picks or characters that have a reasonable amount of support for being playable, please - I don't want to see people saying things like "I'd pick Geno because I want to make his fans upset" or thinly-veiled excuses for bashing a character, or saying that they won't be included, or that a Mii costume would be the closest that they'd get to being playable)
I'd go with Emil from Nier and Nier Automata.
I think his design would work well for being a Mii Swordfighter costume (with the giant head that Yoko Taro wears as the mask, and using his staff as a sword like what Viridi does), and even if 2B can't make it in for Good Boys And Girls reasons (though they could change her design a little bit like female Corrin's if need be), we could still get at least one song from Nier Automata in the game.
...though in a bit of a Monkey's Paw situation, it would probably be this.