I can imagine this being used with some form of acoustically hardening resin. Put it in a container where the walls are ultrasonic transducers and then make the wave interact in such a way as to create acoustic hotspots that harden the material
I've thought this would be cool to with radio heating. The wavelengths are smaller so you should be able to get better accuracy
I don't think that's even necessary! You could use this acoustic technique to shape ordinary light-curing resin and then flash with UV light to harden it.