Soundwave on 25 May 2015
It's not there's some rule on high that there can be only one Mario Kart per generation either.
NX could have Mario Kart 9, and then Mario Kart 10 two or three years later. I don't see the issue, if you can have Mario Galaxy 1 and 2 or Zelda: OoT and Majora's Mask in one generation, then two Mario Karts certainly shouldn't be out of the question.
