Is it too much to ask for Peach's Castle AND Hyrule Castle? Universal needs its own castle, so why not two? I'll also need a Pokemon Center/PokeMart hybrid, Samus' ship, and the Mario Kart track seems like a given so I'll add that, too. And how about a walk through attraction for level 1-1 of Super Mario Bros? I don't think all of that is too much to ask...
So yeah, let's build a third park.
And JungleSkip hit the nail squarely on the head. The current console wars are meaningless in this regard. Name one Xbox or Playstation character that is more widely known than Mario. It's a trick question because you can't.