Well, all the VFD I've seen have a
sine-wave AC output of varying frequency, which is much more complex to do in such a small package as the ESCs we use.
IMO, ESCs are just too physically small for the currents we use to be able to design a true VFD, not to mention the inefficiency of creating the modified sine wave output. I think the best we are going to be able to get for a while is a "VDCFSWD" (Variable Duty Cycle and Frequency Square Wave Drive).
