[sitkack]

Exactly. The B field can be cranked up for short a duration to maximize torque. The rotor could also have much lower inertia.

I sketched out this same topology, with inductively coupled coils for the rotor's magnetic field. If you don't need the fields to reverse (they wouldn't with a magnetic field). Then you could still have small PMs in the rotor with a coil to provide boost field for additional torque during acceleration.