The only other prior art I know of is
Toda, I. W. A. O. (1980). DCNA higher level protocols. IEEE
Transactions on Communications, 28(4), 575-584.
wherein they state the following:
A virtual file system, from the viewpoint of application programs on a
computer, models the file system functions of other computers. This is
done in the same way as with virtual terminals, a virtual file system
consists of a UPP having virtual files (VF), and a UCP which executes
virtual file system protocols.
I'd be interested if you find anything earlier.
Anthony