first i will start by saying that I hope they use MK8 DX as a platform this gen and just keep giving it more DLC. but if we need to get a whole new Mario Kart game in there, it should have the following -
-Remove Characters: Tanooki Mario, Cat Peach, Pink Gold Peach, and Baby Rosalina. there is no reason for them to exist and nobody wants them as playable characters. they have degraded to joke characters that just stop the game from being considered perfect.
-Add Characters: Diddy Kong, Funky Kong, Birdo, Petey Piranha, Paratroopa, Goomba. all of which have either appeared in past games and are not presently there, or are just staple Mario characters who would be great additions to the roster
-16 new courses, 16 retro courses, 16 bonus courses. If MK8 can give us a new standard of 48 tracks, then thats what i want from here on out