But even IF your prediction on power is true (WiiU 1.8 to 2.2 times as powerful as 360 and PS4/Xbox-3 9 to 11 times 360) that still wouldn't be anywhere near the same hardware gap as last gen with Wii vs PS3/360 (360 is at least 10 times as powerful as Wii). Also as people have said here in the past Wii's old graphics architecture was the biggest reason it got so few of the big multi platform games, not power. A game designed for a GCN DX11 based GPU isn't going to be difficult to get running on a R700 DX10.1 based GPU (if WiiU's GPU is really based on that). I mean plenty of PC games will run on both, the same couldn't be said for games designed around DX9/10 and the DX7 level GPU in Wii.
My own prediction is that WiiU will be more like 3 times 360 and the next Sony/MS consoles will be 2-3 times as powerful as WiiU.
A 5x gap would still be big enough to hinder it greatly. Bringing up PCs is pointless, since consoles are the lead platform 99.9% of the time, and you're also forgetting that PCs will keep advancing as well. Many serious devs will be frustrated if 2009 tech holds back their 2013 machines, and then further holds back their 2016 PCs. On the consumer side, Wii U games will look a lot worse than other versions, which may affect the experience enough that most people will just buy one of the other consoles. Then Wii U multiplat games won't sell enough to be worth it, and support will dry up. The only way Nintendo could partially avoid this would be to give Wii U a 4-year life span.
Wii U won't be "safe" unless it's 5x the current gen while the others are 10x or less. 8x the current gen is the absolute minimum we'll see from Sony and MS.