Minimal resolution rear view camera for cyclists, Pop-up labels on sticks for landmarks while hiking, Overlay constellations at night, Overlay navigation path for hikes, cross-country skiing, products in shopping centres, ill relatives in hospitals, Navigation overlay for watercraft, predicting safest route, best route based on long term wind direction, avoid larger less-maneuverable craft.

I'm surprised GPS hand unit manufacturers haven't implemented a beeper that beeps once to veer left and twice to veer right when following a loaded route where there is no obvious path i.e. snow.

I think we don't have more navigation 'helpers' due to legal liability, you wouldn't sue your friend who got you lost but you might sue a GPS/glasses software vendor.