Koopa the Quick is the giant Koopa Troopa that is found in Bob-Omb Battlefield and Tiny-Huge Island in Super Mario 64. Mario has to compete in a footrace against him. If Koopa the Quick is in the game, I would expect him to look like the Koopa Troopa character in the SNES version of Mario Kart, with the only difference being that he would be in the same size and weight class as Bowser, Wario, Donkey Kong rather than in the Toad range.
While I hate to rain on anyone's parade, I'm almost positive that the list of characters on NintendoNow is bunk. I'd be truly surprised if their list turned out to be anything but a fraud.
Edit: Wesisapie -- No, to my understanding Nintendo got the rights to everything in the Donkey Kong universe -- including the stuff that Rare created.