Oooooooooh. An idea is aborning....
How about allowing filers admins to specify the protocol capability profile that a client is allowed to see on a client-by-client basis in a file not unlike the name-mapping files and exports files and quotas files that we already use...
Then we could have NFS-over-TCP turned on for WAN clients but turned off for LAN clients and can experiment with NFS3/2 - all by configuring at the server end (one place) rather than at the client end (many places).
Thoughts?