Over and above foveated rendering for improved fidelity, this sort of eye tracking will allow for super precise interaction with objects.
Think to the levels of choosing a marble out of a jar. With old tech it would just stick an object to your virtual hand based on some predictions - and design had to consider object density in the world to avoid frustration, now it will know exactly what you’re wanting based on your eye.
Probably a lot more that can be leveraged we haven’t even considered yet.