You're right about it being hard to think up new tracks. That would be a challenge, but on Super Mario Kart, many of the tracks were sorta taken from Super Mario World. I would think that we could take ideas from the latest Mario games and make them into tracks.
As for other things like characters and items, I don't think that would be to hard. We could keep most of the original drivers, and maybe make a new one. For items, we could just take from different Mario games.
Bowsa