Very cool!

I can see this quite useful for educational demonstrations of physics situations and mechanical systems (complex gearing, etc.). Also maybe for product simulations/demonstrations in the design phase — take output from CAD files and make a nice little 3D demo.

Maybe have an "inertia(?)" setting that makes it keep turning when you move far enough off center, as if you were continuing to walk around it.

The single-viewer limitation seems obvious and fundamental, and maybe a bit problematic for the above use cases, such as when showing something to a small group of people. One key may be to take steps to ensure it robustly locks onto and follows only one face/set of eyes. It would be jarring to have it locking onto different faces as conditions or positions subtly change.

Good ideas - we've considered these as well actually!

The intertia-idea wouldn't be too difficult to implement, but its usefulness would probably depend on the application area.

Yep exactly. Usually it locks onto one person's face but it can also jump around, so there are still optimizations we can do there - but generally it's supposed to be for one person. If you compare to VR headsets, two people can't wear the same VR headset anyway!