I would start with a simple test if more than 4 wheels on a kart can be done. Tracked tyres may also be a problem since the wheels a seprarate objects.
I guess we would be talking about version 1.x or something if no one else steps in and do the work required - kart with 4 wheels and motorcycle with 2 is just a tiny little bit far from each other in terms of physics.
Hey pal, I took an oath for justice! "In happy days or tightest tights..." or something like that.
Also, the front end would have to be animated to rotate (steer) with the turn.
I was afraid it wouldn't be easy. I do think other types of vehicle should eventually be supported, but it looks like the physics will need to be redone first.