I expect to see Wii 2 around November 2012, and the other two manufactures to follow in a year's time, if they want to or not.
The Wii2 will steal a lot of 3rd party exclusives because it's the new thing, and with the brand name and franchises behind Nintendo, Sony and MS don't want them to get a lead at all. It'd be stupid. So MS and Sony will be forced into the next generation against their will IMO.
We'll see. E3 could, but won't, be interesting...