Do you have any thoughts on why this hasn't seen mass-market adoption? Any major downsides? I have never ever heard of this technology or seen it integrated into the speakers of the big companies in this space. But looking at it just makes me go WOW.

Perhaps it's the lack of bass? For string music and spoken word ultrasound directional audio is fine, but for most music it's not really appropriate.

Imperial War Museum in London seems to employ something like those in their exhibitions. They have black rectangular plates affixed in various places with very localized sound fields underneath them.