One thing I would like to be able to do with the proxy server is have a whitelist and blacklist of local IPs, so no one can accidentally DoS a conference running on the same server, or find themselves with a non functional proxy (and a lot of head scratching!), because the UDP ports are being used by a conference. If they connect on a blacklisted IP, the proxy would simply issue an error saying connection is not permitted (since the TCP side can safely be opened, this should work).
Proxy servers do not issue error messages. They only thing they can do when they don't want your connection is to simply close it immediately, or refuse it entirely. You can solve that in the firewall.
However, when you want to reserve a proxy for a conference or other usage, you can simply set a different password than PUBLIC for it. That will make it a private proxy which can only be used by a user or service who knows the password. (and it will not appear in the proxy list)
Rob