Has any form of UNIX (ignoring POSTIX compliant OS's that have an internal
structure unrelated to Linix / BSD / Mach / ... like OS2 / etc..) ever had
any kind of registry (for the core OS, not the applications; system daemons
may be tracked by such a structure -- but not user daemons)?

The Apple OSX (but not really AIX) and RTOS variant QNX, as well as BEos are
about the only substantial deviations from Unix in the modern era.

Not a one has any kind of registry data structure that I am aware of.

With respect to modern Plug and Play issues, and some aspects of booting
up -- a very limited registry would have some utility. There may even be
some IEEE or ACM papers on variants of Unix that have tried this. I am not
suggesting the concept be applied to Unix (non Intel) workstations or
minicomputers.

I am not suggesting any design like anything in the Microsoft mold, just
something to make storing and recovering (if necessary) core OS states more
robust.