Personally I'd like to see the monolithic Unixes get decomposed into multiserver, as was attempted with the IBM SawMill project in the late 90s for Linux.
Personally I'd like to see disjoint drivers and operating systems. No single OS model solves all problems. Of course no driver code scales to unlimited uses, but at least steps should be taken to ensure that current driver code goes as far as it does. (Then again, I already did that, now just putting my mouth where my money went)
Personally I much rather like the approach Plan 9 took to decomposition vs what SawMill attempted.
Going the Plan 9 way would be a blank state reset of everything, doing a retroactive modularization would retain the existing environment.