Server exports

Some factors which may influence design of server exports:

I'm told there exist sites (using Solaris server) with as many as 10k exports, with as many as 1-2k active at a time.
v2, v3, v4 should normally all see the same namespace. (Not currently the case!--see pseudofilesystem improvements)
It might also be convenient to allow arbitrary remapping of exported namespace. (E.g. to make /export/1 visible to clients doing mount as /usr/local.)
People occasionally want to be able to take filesystem offline temporarily without losing clients--so export shouldn't pin filesystem. (Currently they can do that by stopping mountd (?), flushing caches (exportfs -f), unmounting, then remounting, restarting.)