Honorable Mentions: Satoru Iwata, Reggie Fils-Aime
Shigeru Miyamoto is perhaps one of the most well known video game creators of all time. From games like Super Mario Bros., The Legend of Zelda, and Star Fox, as well as a plethora of other games, Shigeru Miyamoto has become a household name for most gamers.
Of course, you could just make a Mii character of Miyamoto to use in the game and call it a day, but that would be a missed opportunity. At E3 2015, the Nintendo Direct presentation included puppets for Shigeru Miyamoto, Satoru Iwata, and Reggie Fils-Aime, created by Jim Henson Studios. Muppet Miyamoto would fit right in as a Mario Kart character, and would easily translate to the games more cartoon like graphical style.
It may be a long shot, but it would be cool to see this acclaimed video game creator appear as a playable character.