This game I made some time ago could take advantage of the eye tracking technology:
https://play.google.com/store/apps/details?id=com.rmxxabes.giantheadinthesky
This is a short game for Google Cardboard that uses the gaze as an input method (you look at the crystals to activate them). Removing the targeting circle in the center, and actually using your eyes to interact, could be really awesome.