First of all, full disclosure: I really do not like the name Wii U. However, I'm open to Nintendo keeping the "Wii" name if they feel that it'll still attract the casual audience. However, I believe Nintendo has said that they hope to capture both the casual and core audiences with the Wii U. Unfortunately, herein lies the problem that I see with the name "Wii U". It seems the "Wii" name has lost it's "cred" with many core gamers, so they run the risk of continuing to alienate those who wouldn't give a system with a name like "Wii U" a second thought. On the flip side, Nintendo made so much money in the casual market with the Wii that they hope that it's brand recognition will continue to resonate with that crowd. The downside there is that, and correct me if I'm wrong, but many of those new casuals who purchased a Wii did not continue to purchase much software throughout the rest of it's tenure, which really makes me wonder how much of that demographic will bother to embrace the "Wii U", especially if the name does little to differentiate it from the Wii.
Nintendo is in a tough spot with trying to please both crowds. They're best bet might be to try and find a name that had the same impact of "Wii" -- ambiguous yet recognizable -- that won't scare away the casual crowd nor deter the core. Perhaps it will be new and exciting for the casuals, yet maybe with the hint of edge that long lost core gamers crave. Personally, I would just be happy for it to change from "Wii U".