Very interesting motor design. It is not exactly ironless, since it uses powdered iron magnetic components which have lower losses at the 300 Hz frequency. And it also uses permanent magnets. Both of these components are fairly expensive, fragile, and susceptible to damage from heat. I guess that is why the motor is liquid cooled.
It would be interesting to compare the performance of this motor to an induction motor made from thin high quality laminations, and run up to maximum speed. My guess would be that a 95% efficient
standard three phase motor, carefully rewound to about 150 volts and having 6 poles, could be overclocked to 180 Hz at 450 volts and attain 3x the power at about 3x the losses, or 85%. Still very good.
I would expect a motor made from special laminations could be run at much higher frequencies, probably at least 400 Hz. I have done testing on a toroidal transformer which uses similar tape wound laminations as its core, and it seemed to perform well up to 16 kHz. The magnetization current actually dropped at the higher frequencies, although higher voltage would cause them to increase. I know an induction motor is not the same as a transformer, but there are similarities.
I have also wondered about the possibility of making a motor with ferrite components. That would possibly allow the use of 20 kHz or even 100 kHz, which would mean that the motor would need to have something like 200 poles, or else it would run at 1200000 RPM! Even 200 poles would be 12000 RPM at 20 kHz, but that would be workable. And of course a PWM drive would need a carrier frequency close to 1 MHz. But that is far out stuff and way off topic.
[edit]
You posted while I was composing my post. For as many years as I have been proposing 360 or 400 Hz motors, I'm surprised I have not coma across that website before. But it seems odd that their only vehicle motor is a big 200 HP job while 50 HP would normally be enough, especially if you can boost the torque for short durations. I don't know why you would need their special controller, although most standard controllers might not be set up to allow the appropriate motor characteristics. Some of their lower speed motors must have 24 or more poles, while the highest number I know of for a standard motor is 12. That's how many poles I used for my design of a 3-phase 8 VAC motor which I wound on a 36 slot stator from a 1/2 HP single phase fan motor. I don't know why other companies don't join the bandwagon and offer similar motors, at least maybe 180 or 240 Hz.
Actually, rereading the website, it seems that the slower motors have gearboxes. A 2 pole motor at 400 Hz is 24,000 RPM, so their 6000 RPM motor is 8 poles, and all slower speeds use gearboxes. A 12 pole version would be 4000 RPM which would be just about right for an EV.
Thanks!