I used to have a roommate who, when he received an electric razor for Christmas, immediately disassembled it and reassembled it. I suppose that's the sort of person who works at Slashgear, where they have published a piece describing what they found when they took a Wii U apart.
The most notable discover of Slashgear's was that the battery case for the Gamepad is large enough for a bigger battery, suggesting a) that Nintendo may have shrunk the battery to trim cost, and b) it's possible someone will come up with a gamepad battery that gives more than four hours of play.
The site gives the Wii U an "8 out of 10 for repairability," meaning that it's apparently pretty easy to take it apart and fix any problems. My roommate would have loved it.