My take on the Wii U -> PS4/XB3 power gap:
Given the rumored specs for PS4/XB3, both Sony and MS are probably looking for a 10 year life cycle to recoup R&D costs over the long run (If the 2014 release date for XB3 is true, then the 360 would have been around about that timeframe). But I believe Nintendo is aiming for a typical 5 year cycle for the Wii U.
So for the first 1-2 years, Nintendo will have the only “next gen” console. It will probably then take developers about 2 years to fully tap into the true power of PS4/XB3 (outside 1st party efforts and 3rd party exclusives). Until then, the Wii U should be able to handle ports well. But once this time hits and the Wii U no longer has what it takes to handle the ports (or the ports would be so watered down that developers wouldn’t bother), it will be time for Nintendo to unveil their new hardware anyway. At that time, they should be able to produce hardware than is more powerful than Sony/MS' (but not drastically so) at a reasonable price.
Then, Sony releases PS5/XB4 a couple years later and the cycle repeats.
For this strategy to be more effective, the Wii U would have been released last year. Unfortunately for Nintendo, the 3DS was struggling and releasing the Wii U while trying to proper 3DS may have been too much for them to handle.