No, not common, but as the OP noted the evolution of MEMs based microphones might make them a lot more common. As the author notes, they are more like holographic cameras than what many people think of as "regular" cameras. By converting the imaging into the FFT domain the resolution gets better "everywhere" the more sensors you add. (If you have ever cut up a hologram into smaller and smaller pieces you can see this in action, as the full image is still there, just lower resolution). It would also be interesting to illuminate a non-active source with sound beam. By using two, slightly out of phase, ultrasonic sources he might be able to reveal depth detail of the surface being imaged.