We have had a CoTech XMPP server running for a while as a part of the CoTech Nextcloud server, but it has hardly been used as far as I’m aware. You can access it using your Nextcloud login with a XMPP client, or using the Nextcloud web interface, there is the ability to create private channels/rooms for only people with CoTech Nextcloud logins and also the ability to create channels/public rooms that people on any XMPP server can join.
At the last CoTech event in Newcastle several people asked me if we could setup a CoTech rocket.chat server — do people think that this would be worth a try?