S-iv eye scrolling?

I had a Canon camera 10 years ago that would follow your eye as you watched the viewfinder. You could look at an object in the viewfinder and the camera would focus on that point. Look up quickly and you would get a depth of field preview. The challenge with the phone (in my mind) is monitoring the eye from the phone which is a fair distance compared with an adjacent eyepiece.
 
Eye phone vs iPhone
 
This is a cool idea!