This is Mario Kart Tour's line up of alternate characters so far. And after this variety, I can't go back. They need to embrace this aspect of the game with the next mainline instalment, and keep on adding costumes in updates to go alongside holidays, game releases etc.
I will say though, they need to not treat each costume as it's own character like Tour does, as watching 8 different Mario's race is not something I want to see.