With only rumors to go on, I'm afraid I can't write about Microsoft and Sony with much confidence. But I do think that the next versions of Microsoft and Playstation won't be much more powerful than Wii U.
However, I agree with you Danne about this: if either Microsoft or Sony try to make a super-powered console and the other chooses to be closer to the Wii U in terms of power, I think the super-powered console will suffer.