Some team of sneaky beavers out there got Mario Kart 8 to run almost perfectly on a Wii U emulator for the PC.
Since October of 2015, the team at Cemu have been steadily chugging along at their Wii U emulator for Windows PC's, but don't get your hopes up if you're looking to play some Smash on PC anytime soon. Even the most current version of Cemu barely launches most games in the Wii U's library, let alone play them in an acceptable fashion. The developers have patched and improved the emulator about twice a month since its inception, but most of the work has been mostly on basic functionality of the program.
However, this very successful test of Mario Kart 8 may be an indicator that progress on the Wii U emulator is very promising.
This isn't the first time that a Nintendo console has been successfully ported into a PC environment. The Dolphin Emulator, initially released way back in 2003 with a stable version finally released in 2013, is a GameCube and Wii emulator that works almost perfectly. Unlike the current version of Cemu, Dolphin can run most of the existing Wii and GameCube library (save for a few outliers).
Despite Nintendo's disdain for these developers and platforms that mimic their hardware, machine emulation is completely legal. The legality of ROM's however is tenuous at best and downright illegal at worst, so while projects like Cemu and Dolphin are technically legal, in practice playing actual Nintendo games via these programs is not an activity that Uncle Sam approves of.
However, if you own a physical copy of the game you can dump your own personal ROM onto your computer and run it through an emulator legally. Check out the Cemu website for details here.