So you can get a prometheus alert over Cisco Jabber? FWIW, I've found that prometheus alerts to Slack have been quite useful, but we include a link in the message to Alertmanager, to silence alerts that are not meaningful. We aim for median 1 actionable alert per day.
How in-use is XMPP these days? Are there communities built around it like IRC/matrix? Are there common services that play nice with open source XMPP clients?
You are probably using something that builds on it. It's the IETF standard for IM, scales very well and it still seems to be the industry standard for large messaging systems (WhatsApp, Zoom, Jitsi, Nintendo Switch presence... are known to be using XMPP).
Cool community projects which also care about the federation aspects are jmp.chat, snikket.org or movim.eu (a federated social network built on XMPP PubSub nodes that broadcast ATOM items). There are communities that are on XMPP, but I currently use it mostly for friends and family.
I've spotted a few decently large, but foreign (mostly German and Chinese) hardware and electrician communities on XMPP, but as I'm not multilingual I couldn't tell you how good they are.