The paper from microsoft shows that with a fast eye-tracking device (300Hz) and a resolution of 1080p you can have a 4-5x performance boost and you see no difference from a normal rendering image! Its massive. With a 4K resolution you will have an even higher performance boost.
Your Eye can only see max. 2 Degree of your field of view. This is your focus point which will be rendered with high resolution. The Eye can move up to 900 Degree per Second and while it moves you see nothing.
Foveated Rendering is possible and it will be important for the Oculus Rift and other HMDs, because you will never render 4K at 120fps. (i have an oculus rift with integrated eye-tracking)
I have the hardware my problem is the software side. The Problem is that i need to change the renderer… 
If I can setup cameras with different resolutions and different quality settings, i can render 3 images and try to blend them together.
I need your help.
Johan Andersson from DICE speaks about that: