Not sure how much that would help. Amiga had a ROM chip with a large part of the o/s on and that wasn't entirely a huge speedup.
Solid State speeds have come a long way since then. Think of how fast pdas & mobile phones boot up, its practically instant (and some of these have far more 'bulk' than the original amiga os).
Something as big as windows or ubuntu would take some seconds of course but it'd be damn sight faster than magnetic media.