4 mics and a computer to produce 3-D model of room

This is awesome! I wonder if the algorithm is going to be open source as I could see it being very useful to budget-constrained organizations such as http://publiclaboratory.org.

Cheaper than indoor LIDAR?

First reaction: wow. We are all walking around with fat low-power parallel processing in the form of smartphone GPUs already. A little effort and we can 3D model anything with touch. VJs and other artists of the future will have the true canvas of reality to remix, collected casually in realspace and projected/manipulated in as many dimensions as required.

Reality check. While on the face of it this is potentially huge, let's look at limitations.

The biggest limitation is that it is indoor. Sounds that don't return in the vastness of a field or desert tell you nothing about the space.

Secondly, many conditions can complicate audio collection, including wind. This makes using the technique from drones or other elevated locations somewhat more difficult. Also you are out of luck if you have .. say .. noise-dampening curtains hanging around the room, for instance in a concert hall.

Thirdly, there will be lots of gaps .. for instance standing in the 'head' of a mandlebrot-set style shape comprised of two conjoined circles, the majority-space (or at least portions thereof) would be very unclear.

Fourthly, actively producing sound can be polluting or undesirable and .. failing that .. it would seem that individual, distinguishable sounds are not always present in all environments.