HappySqurriel on 24 November 2012
In reality? Probably nothing ...
I suspect Nintendo wanted to keep the "Wii" brand, wanted a short name that would work in multiple languages, didn't want to use numbers or imply that it was an "improved" Wii, wanted to avoid using familiar letter combinations or cliche's, and they wanted something to make it easy to brand their games (New Super Mario U)
It probably came down to a handful of options and they picked "U" for some reason
