I'd be neat to have information displayed while driving a car. A subset of information currently displayed on a dashboard would be an obvious first choice (speed for one).

You could also maybe perhaps tie in a car's knowledge of adjacent vehicles, which is something I've wanted for ages. Since some newer models have some level of awareness about the speed / distance to / relative location of cars around your car, you could eg overlay the speed/acceleration info onto adjacent cars, so you'd know if you'll need to pass or speed up. Seems at least possible since the glasses have awareness of your head's orientation, something missing from any existing windscreen-style HUD system.