The next generation, or 8th generation will start, in 2011 at the earliest. Both MS and Sony are losing way too much off their consoles to simply just end it now. They have to wait out awhile in hope of profits.
Nintendo on the other hand probably was going to end at that time anyways. I wouldn't see them going much longer than 2011 with the Wii.
What Nintendo could do though is once Wii gets a large and secure lead quickly immediately have another console ready and release it and this would totally disrupt the competition especially if it not only pushes motion sensing and other innovations but hardware as well. If Nintendo controls this generation then it's very possible that they'll control the next one as well.
But 2011 is where I see the change happen as that's when I see Wii having the controlling lead to make such a change.
