I wonder how hard it would be for the digital eyes to track your actual eyeball motion.

I guess it would be tricky to fit an optical sensor under that under the mask, but maybe you can track eyeball motion by tracking the muscle movement around the eye?

Some quick tests (i.e. placing my hand on my face and moving my eyes around wildly) suggests that it might be doable. :) Possibly just by tracking how your nose twitches...