Legend of Zelda
Link appeared in Mario Kart as did Hyrule Castle but come on. That was barely a cameo.
I think Legend of Zelda having so many games and such a wide variation of stories, art types and memorable characters more than qualify it for the kart racing treatment.
Not only does the Legend of Zelda franchise have a ton of iconic areas that can be used for tracks, like mythical forests, rock slide prone mountainsides, volcanic lairs and so many different castles, but it also has various art styles that can make tracks get some extra variety. The misty forests of Breath of the Wild is vastly different than the colorful bold forests of Windwaker or the shiny plastic look of the Link’s Awakening forests. It’s filled with clever ideas in location and appearance.
The franchise is also filled with a wide variety of characters from the Four Champions of Breath of the Wild to bizarre characters like Tingle. And Hyrule Warriors showed just how easy it is to create a story that justifies characters from various games coming together for a common cause.
The vehicles may be a little hard to come up with at first until you remember that Breath of the Wild’s entire thing was based around a civilization that made mechanized salamanders, spiders, elephants, etc.
Power-ups can be anything from boomerangs, wind gusts, arrows of light and Bombchus. Characters could even have personalized attacks like the Zora Princess causing a large wave of water carrying her forward and slamming into opponents or a Gorron turning into a boulder. Zelda casting magic or Tingle…just being Tingle.