[mmooss]

A relatively simple generic device, mounted on a car's interior ceiling, seems possible: It would project light 'dots' below onto everything the user looks at. Using the car's momentum, the dot movement could be mechanical, though you'd need power for the light.

Not every passenger would want to see the dots; their range could be restricted to the user's seating area or narrower - the user placing objects under the dots as needed. Also, of course the device could be turned on and off.

The dots need brightness and color visible on different surfaces, but those could be easily user-adjusted. Also, I wonder if a grid would work. (Edit: For use with screens, possibly the background reflection of the device, with its grid of lights, would work.)

The real question is, would it work? Does Apple's solution generally work or is the OP just a happy anecdote? Is there more magic to Apple's solution than dots swaying with momentum?

[ssl-3]

There may be a way to do this with a point-source light (a focused LED, or maybe an appropriate laser), and a diffraction grating (which may be already exist in stage lighting world). Such that when the parts move relative to eachother, the projected dots move across the car's interior.

In terms of controls, it seems likely that it should seek to emulate whatever it is that goes on inside the inner ear, so that the input from our eyes better-matches the input from our ears.

I don't know how Apple's dots work (and I don't think my singular iOS device is new enough to try), but if they only respond to acceleration, then doing it this way should help establish mechanical limits: The acceleration (in any direction) of a car is finite, and always returns to zero.