I suspect it would be a very challenging problem for the earpiece part to recreate the directional info as well as our own ears, since the brain's ability to detect the direction of sounds depends on the shape of the ear itself.

Maybe a simple mechanical clicker device like those used for dog training could be a useful tool.

I have one of these - purpose built for blind people to use. Pretty sure I picked it up at a NFB convention in Atlanta around the turn of the century. (NFB = National Federation of the blind)

How well does it work?

I will get back to you on that. I just found it in my desk. I myself am sighted, and have never used it for echo location - yet. Looking at it I realized that it was given out by my old employer: Blazie engineering. Coincidentally, I just ran into the founder recently. Next time I see him, I will ask him about the feedback he got on these clickers. I will say that after twenty years in a drawer it sounds good to my uneducated ears.

please ask them if this or any others were commercially available. Thanks!

Seems like a fun use case for spatial audio on the airpods.

If the wavelengths are not far from audible, wouldn't it be mostly a translation?

See here: https://www.youtube.com/watch?v=PD3Y1l8XyUw

Another route would be to mix the ultrasound with another sound closer to the ear, then there is no need for an electronic ear at any point. The interference between sound can cause the inaudible frequencies to become audible.

Just on this topic, would it be possible to make a whistle to do the same thing? I.e. crafted so it emits both ultrasound, and the audible counterpart which interferes with it to make the return audible?

Perhaps it could be such that the ultrasound warbles whilst interfering sound does not (or vice versa), which would make the sources easier to distinguish also.