Nintendo didn’t hide its policy that blocks gamers from logging into the Nintendo Network using a different Wii U. But the company has changed its stance, as it recently stated it’ll be possible in the future, and won’t even be limited to Wii U, but will also be accessible through PCs.
Nintendo had formerly said it wouldn’t allow such access:
A Nintendo Network Account can only be used on the console where it was created. In the future, you will be able to use your Nintendo Network Account with future Nintendo consoles and other devices, such as PC’s.