For as long as there are consoles there'll be hackers and programmers attempting to reverse engineer them for emulation. Due to all of the work platform holders put into closing off their systems it proves to be difficult, and it took quite some time for the infamous 'Dolphin' emulator to make Wii games playable on PC. It's a niche area, and in the current generation the sheer difficulty of running emulation means that it's unlikely to lead to widespread piracy.
Now, just three years into its life, definitive proof has been shared of a functioning Wii U emulator, which the creators are calling Cemu. These sorts of emulators often take years to come together and even more time to optimise, and the first version of this particular example seems to be legitimate; yet based on the comments of those trying it out is far from playable or functional on a meaningful level. Those deep enough into the scene to have dump files of Wii U games have been testing a host of retail titles, typically reporting load times of multiple minutes and crashes after initial screens.
In any case, it's demonstrated to be functioning below (we're not sure how long this video will be live).
Is this a threat to the Wii U's retail position? Not really, and we must consider how the Dolphin emulator was a niche concern that many Wii consumers never even heard of. In addition it'll likely be a couple of years or more (based on how other emulators have come together) before this is functional on a meaningful level, and by that point the Wii U may have been phased out at retail.
Beyond all of that it's proof - along with 3DS homebrew efforts - that hackers and programmers will always try to work around gaming systems. Cemu is the latest in a long line of attempts.