FOr the ultimate in shortness I'd get a pancake motor and grind a
cutting point on its shaft. total length, including bit, under an inch.

This would be nice! I don't need to drill. I want a really squat
rotary sander but not the type described as 'orbital'

I needs one that forcefully spins rather than vibrates as the target
material is jelly-like and just absorbs the vibration displacement of
that type of sander.