No, that's not how Nintendo does things really aside from DKC 3D. They always make one Mario Kart and one Smash Bros per generation. There will be no MK8 port to 3DS at all so stop hoping for one now.
You're talking about porting down a game from a multi-core IBM CPU @1.24Ghz, 1GB DDR3 RAM and on a 550Mhz GPU in the hundreds of Gflops range, running at the very least 1368x720 to a dual core ARM, 128MB FCRAM with 6MB VRAM and into 400x240.
That literally can't happen. Mario Kart 7 still sells very, very well for them so there would be no point in making anymore Mario Kart for 3DS since that game will likely be a steady stream of pure profit for the next few years.