In a DLC Update to MK8 there came an option of choosing between different colours for Yoshi and Shy Guy, but not for Toad and Koopa Troopa. Hopefully that can be incorporated into the next Official Mario Kart game. Another thing that should be a first is outfit choices, Mario could have a select of different outfits he wore over the years and in Super Mario Odyssey, and Wario could have his Biker Outfit from the WarioWare Games. For however they do turn out, it's safe to bet that these Alternate Outfits won't be available from the get go, and have some sort of unique unlockable aspect.