Plan9 in fact uses file descriptors all over the place, including accessing synthetic or real filesystems (which are really namespaces). In fact the only "globals" are the #<dev> devices.

IMHO you're better off starting with plan9 concepts + pure capabilities (KeyKOS as opposed to Capsicum). It would not enough to have a clean architecture unless a) it matches or improves upon performance and b) there is a way to run existing Unix software via some adapter layer or library or monitor.

I suspect if you try to "reform" unix, there will be a lot of recidivism :-)