Keep in mind higher frequency induction motors are smaller and lighter-and can run at higher speeds.This is common in aircraft applications.IE a 2HP 400Hz motor is about the size of two large fists placed end to end.I saw this motor in a fighter aircraft-used to drive the planes 20mm nose rotary cannon.Now we all know how big a 60Hz 2 hp motor would be.Not practical for this use.And the planes generator would be larger and heavier as well.And these motors can be more efficient than their 60hz counterparts.BUT 400 hz and other higher frequency power supplies don't transmit well over long distance like 50-60Hz or the 16-25 Hz would.Think AC will be around for a long time-DC doesn't transmit well unless synchronous convertors and rectifiers are used-this is EXPENSIVE.And with SS its easy to rectify whatever frequency of power you are using.