No 3DS plans at the moment
When the PC version of Mutant Mudds was announced with extra content, 3DS fans everywhere let out a high pitched shriek, hoping to get that content at a later date. Renegade Kid delivered, but that may not be the case for the Wii U version of the game.
After being asked on Twitter, developer Jools Watsham stated that "The current plan is to make the Wii U content exclusive to the Wii U." Well, there you have it folks: if you want to experience the unique content of Mutant Mudds on the Wii U, you'll have to...own a Wii U.