There are motors with peak efficiency about 90%. The first one of those I ran into was fifteen years ago. Which means not only is it possible but the patents will have expired, if not now then soon.

Power density has gone almost too far. There’s one pancake motor I’ve seen recently where the shape of the enclosure is dictated by mounting concerns. You have to be able to mount the motor to something it can’t tear apart. If they shrunk that motor another 20% then it would be half housing. I’m not sure where you go from there. Thinner? Motor per wheel?