Say, want to transfer that Nintendo Network Account to another Wii U
if it happens to break down? You can't, for now. It seems your Network Account is tied to the physical machine so there's no going to someone else's house and logging in as you on their Wii U.
Seems a little backwards? It is. Now, let's hope this is something temporary as not every console is 100% defect free and sometimes they have to be replaced. It's easy for the other consoles to login to a brand new one and transfer your items over. If for some reason your Wii U breaks down whether by "natural" causes or an accident, I wonder how Nintendo's going to handle the situation where someone buys a replacement.
It seems they would be in a rude awakening if they aren't able to get the items they purchased online as well as their profile to a working machine. Nintendo's always been behind when it comes to online capabilities as well as ease of use. Hopefully, they have a contingency plan in place and maybe they'll be able to adjust this policy soon because you know someone's going to cause an uproar the first time they try and get their new Wii U working with their account from another machine.