The Wii U account (registered to Nintendo Network) is connected with the actual hardware, unlike how it works with Playstation 3 and Xbox 360. Kotaku asked Nintendo what happens if your console breaks down.
"Nintendo of America's repair process includes the transferring of the Nintendo Network ID to a new Wii U console if a replacement system is needed."
Let's hope Nintendo don't get the crazy idea of releasing an updated version of the hardware... but they would never do such a thing, would they?