The idea of turning Mario Kart into “Smash Kart” or “Nintendo Kart” makes me legitimately furious. They haven’t even put in Kamek, Goomba, or Boom Boom yet - the Mario franchise (as well as its 3 main spin-offs) has a huge rabbit hole of characters and neglecting to explore that in favour of putting in more crossovers is just... no. I’d take Geriatric Rosalina, Capybara Suit Dry Bones, or Purple Cummingtonite Waluigi over Samus or Pikachu any day.
Charizard has a surprisingly serpentine flying animation in Ult, which really isn't the direction I expected but it is neat. We also had Raquaza as a boss in Brawl but he sadly didn't come back.