I thought this'd be a cool addition to Filipe's Superkarts. A warp star (maybe the wagon star aswell), where you just sit on the star, it'll be easy to model considering there's already hoverkarts.
Other karts:
Egg-1
Sports Bike (MK8)
Rollerblades
Hoverboard
Airship-on-wheels
A kart which is a judge's podium in court. (I thought it'd be cool ok)
Wheelie Scooter
Wheelie Bike
Toad's Mushroom Thingie (MKDS)
More to come soons
But yeah, some will be easier than others considering hoverkarts have been made already.
I'll put links to complete ones here I guesses