severe bison
As a long time user of tracking products I can't sell this enough.
Currently I am using a Tobii Eye Tracker 5 device (which also has head tracking) and it really helps with immersion.
To name a few examples that other games use it for: Extended view (looking around while not affecting walk direction), interact, aim (triggered when using ADS), throw, Clean UI (items only appearing when looking directly at them), target lock, taking cover and more all at and to the point of your gaze.
Some games even have characters respond to you just by looking at them funny!
I think it would be a great addition to any game.
craggy crown