This is a kiosk system. It's a demonstration Wii U for use in stores. Look at the connector of the big cable on the back of the gamepad. That's either RF video out or to anchor the system so people don't steal the gamepad. Or power like WiiCube says. Probably power.
Demo / kiosk units are special though! The ports on the back of the system are useful for adapting the system to whatever display kiosk you've had for however many years. Kiosk systems also have special software like demos which are worth dumping and examining. I'd guess a firmware image was flashed with those extra ports in the back of the system. This custom case, which is a hole cut in a normal one and a metal plate, is more likely to be from a tradeshow like E3 than a Best Buy or Gamestop. It has a really early firmware version number too.