Interesting.

Needing to run in a specific fluid seems like it could pose longevity issues because a motor inherently needs a shaft to pass out of the sealed enclosure, causing ingress or egress - car AC compressors have this issue.

If you could also make the fluid an effective refrigerant, then this could be good for refrigeration compressors. Those run entirely in a sealed system anyway.

This seems to be a very high torque, low speed motor, operating at 360W 18Nm which means it's 190RPM (20rad/s).

With all the parallel plates, windage friction is going to be very high if they attempted to increase speed, which is usually the easy way to improve power density.

2kV for a fractional HP motor is really pushing things; you would need to integrate the boost converter and inverter into the motor housing. The moment you have cables above 1kVAC or 1.5kVDC, you're 'high voltage' and a raft of new rules applies.