Too late, probably end 2013. Next wii will probably come in 2012. MS is not going to give Nintendo a 3 year head start. They might as well wait till 2017 and skip a generation.
"Heck, this gen was the jump to HD. How do you top THAT jump in visual fidelity?"
Jump to 1080p 60fps with 8x msaa standard. Enable higher lod, longer draw distance, no more pop in. No more need to run shadow maps / transparencies at quarter the resolution or light updates at half the speed etc. You don't even have to change any game assets and you get a huge jump in visual fidelity at no extra cost to game development.
Or is it just myth that pc games with the exact same assets look a lot better.
2013 is enough time to integrate Kinect with the next 360. They probably already have a 60fps hires kinect ready. The infrared camera in the current Kinect is already capable of 640x480 and probably 60fps as well. It just doesn't work with the current 360 due to the USB bandwith limitations.
Ofcourse they can still support the 360. Seeing as how much money the ps2 still made for sony while the ps3 was out, ms would be crazy to drop the 360 like they dropped the xbox.