Nintendo
The route they are going with the Wii U is a dangerous one. They're trying to cater to the hardcore non-Nintendo-die-hard crowd, but so far they've got nothing good to show except a muddy zombie game and a AC3 port that reportedly looks worse than the PS3 version(Which probably looks worse than the 360 version). Sure, they'll sell a couple dozen or more to the Nintendo diehards, but I think the casuals have moved on to other platforms. In 2006 there were no app stores, facebooks, smartphones or tablets and the Wii was something genuinely new - the Wii U definitely is not. The $249 price point is very attractive, though, but that won't help if there is no interest. Another concern is digital distribution - do we have a confirmation that all games will be available through the eShop? I think we're seeing a trend where the consumer expects software to be downloadable, I for one am done with putting a piece of plastic inside my console every time I want to play a game.
Nintendo will do okay but there will be no new Wii, that time has passed and the money's been made.
Sony and Microsoft
So far we only have rumors and speculation on Sony and MS new consoles, but if there is a significant hardware jump there will always be that hardcore who are willing to jump in because of "OMG graphics", but only at an attractive price point. More than 400 dollah for your console, and you're out. Both MS and Sony will probably focus on a pretty powerful machine but also some kind of gimmick, maybe even the same gimmick - I see Kinect stuff is in the rumors alot these days. What's more is that the third party exclusive is dead, but if there is a significant jump in hardware from the WiiU to PS4/Xbox8, the Nintendo system will be left in the dust just like the Wii third party wise. Engines scaling between two generations always ends with both versions suffering. Sony just bought Gaikai, and MS are rumored to be establishing a similar streaming service. These are interesting because people can just try a demo without having to download it, just a few seconds and the demo is starting. You'll then be able to download the full game. I think accessibility will be a major factor next gen. People hate waiting, and the less you make them wait, the more games they'll buy for your console.
MS and Sony will be neck-and-neck throughout the generation.
Edit: Actually didn't answer the question.