GM never mentioned the issues that might rise from the use of PM motors. Over saturation of the PM core can lead to over voltages or other control reliability issues. Occasionally, air gaps in the material left over after manufacturing may have to be repaired. Assembling of PM motors are also fraught with problems, electrocution being the biggest. High performance permanent magnets have inherent structural and thermal issues. As more work is done with PM materials, I am sure the issues can be subdued.