Nintendo's website has confirmed which Amiibo characters will be compatible with Nintendo's flagship racer Mario Kart 8, and as a quick note there is actually both more and less avalible with the game then I was honestly expecting.
The Amiibo characters available are as follows:
Amiibo functionality will be added to Mario Kart 8 with a new Software update next week. Through the use of these different characters you will be able to dress your Mii up in different costumes.
Another theory I have is could we possibly see more DLC for the game in a future update which could include Fox and even Samus, based on the latest DLC it doesn't seem to farfetched, so here's hoping.