I've talked to the owners of 4 major companies on this topic:
- MAC came up with the idea on their own and implemented at some point
- Grin has no interest, asked 2x
- It's been a no from leafbike, asked 3x, thought they would be receptive
- CYC X1 Pro is the only mid drive i know of with very thin lams ( advertised but not confirmed ), makes sense because it spins fast.
- Numerous RC motors spin this fast but consider that they run 10x-50x higher RPM and at these speeds you can get a sizeable benefit.
In DD hub motors you don't see any notable benefits from 0.27mm lams until you are in the 20" wheel size, and that's one of the most uncommon wheel sizes DDs are put in, so no manufacturer got the idea to make a DD specifically for this wheel size, which is ironic because the 20" wheel size is where your typical 9C motor makes peak power/torque/efficiency.
End turn losses are the biggest villain of DD motors so the wider the stator the higher the efficiency tends to get. I think the ol' 50mm cromotor used to hit something like 91-92% efficiency.
An inverse case of that is the
CSIRO motor which is a razor thin axial flux unit with the tightest windings i've seen on any motor. It achieved a peak 97.3% efficiency.
For whatever reason, nobody can be convinced to make a premium hub motor, meanwhile people are buying $500-$1500 mid drives left and right. It's very disappointing the DD has not seen any evolution for a long time.