I think it will be a rather large jump.
If you look at the difference with current tech - Xbox 360 is DX9, and current DX11 looks way more realistic, and the nextbox should at least be the yet unannounced DX12.
And for new upgraded TV hardware - maybe something like a 4K monitor, and perhaps a yet to be developed 3D system.
The next Avatar will be shot in 48 frames per second, twice the 24FPS that has been standard for many years. I predict half the population or so will see a nice improvement in quality/feel. I think more people will so greater interest in higher frame rates.
I could also see support for multiple monitors - like a front and two on the side or the 'wall of information' type experience you get in the Microsoft Store, or the Corning video.
I also think we will see a jump in kinect resolution and reduced lag. It would be able to reach sign langague and could thus act as a tutor for a whole new genre for the consoles.
I like what we have today, and I think the next gen for Sony/MS will have a super, almost creepy upgrade in virtual reality. (but not quite a Star Trek “Holodeck” yet.)