They could re-use the models in the Pokemon Switch game too.

Pauline is not unlikely because she is more relevant now with Mario Odyssey. Kamek would be cool too, I can see him driving a kart.

If its possible then yeah. It could save them the time and money

Plum and Kid from the Mario Golf games...

I would like Cuphead and Mugman so Nintendo and Microsoft: make it happen!

Cloud.And i want a midgar stage and a golden chocobo kart too

Hammer Bro or Kamek or Monty mole in that order. I wouldn't mind anyone in that list, apart from Mona, who can fuck right off!

Birdo... sorely missed since MKWii.

Kamek would be a welcome addition, definitely could replace the Dry Bones slot.
More recent characters like Lubba, Nabbit, or the Sprixies (with pallette swaps) would have been more creative than Tanooki Mario, Cat Peach, or Pink Gold Peach.
I honestly feel that the lack of ingenuity with some of the character roster was the biggest detractor of a perfect score for Mario Kart 8/8 Deluxe (which was arguably the most well-crafted game in the series).

Why not just make a separate racing game that has characters like these and from various Nintendo franchises not just the mario universe as playable characters??? But not the big names like Link, Samus, or Kirby just from the little known franchises or unappreciated characters... And have it star Diddy Kong and call it Diddy Kong Racing 2..