@kenshirriff
Well, the switch to hydrogen not only lowers drag but also the load bearing capabilities (by a lot). Compensation is possible by increasing relative speeds between bearing surfaces and/or decreasing the gap.
Sounds simple, but really isn't.

Nerdsnipe (paper about gas lubricated bearings):
mdpi-res.com/d_attachment/appl

For comparison, modern HDDs are Helium filled to lower the flight height of the read/write head to ~5nm . >>