When asking about eye tracking, always remember "there is no such thing as a free lunch."
Eye tracking is not yet ready for prime time. Only one company so far, the company FOVE has an HMD with eye tracking integrated that is affordable for mere mortals. We are talking the $799 range. Foveated rendering will only halve VR rendering requirements (at its best and most efficient, lens matched shading already does this.)
Why wont Foveated rendering be feasible right now? An eye tracking module needs to have at least a 500hz update rate to track vision well. Even at that high update rate, present Eye trackers have much difficulty tracking your eye's involuntary saccade movements. Even the best eye trackers (we are talking in the 10s of 1,000s of dollar range, used in military and university applications) also require predictive algorithms to make up for the hardware shortcomings.
I hear people ask all the time "what about foveated rendering?" The software and hardware are not yet ready. Even if it were ready, someone like myself, who has Nystagmus would not be able to benefit from eye tracking, nor would people with a whole host of other vision problems.
Now, a foveated display on the other hand, would be a good idea. The startup Varjo is already working on such an HMD, and wants to integrate eye tracking. Most eye trackers today are used for menu navigation. Foveated rendering is a very long way off.
To give you an idea of the difficulty level we are talking about. In our present HMD's we have IMU's to track head movement. Even the best IMU will suffer from drift. In eye tracking you have problems similar to drift.
- Every time you blink, the tracker loses sight of your eyes
- Your eyes (like your head) make micro movements all the freaking time.
No sensor is perfect, and the more accurate a sensor gets, the more you have to worry about jitter. That's why you need all the crazy predictive software algorithms. At the present time, you spend as much computationally to get eye tracking working as you would save if foveated rendering and eye tracking worked flawlessly.