I guess I recant some of my interest in this announcement. I've been on a little expedition of finding a good XMPP server that's capable of clustering, and comparing various offerings. In checking the XMPP Compliance Suite 2020, technically ejabberd Community Edition isn't even compliant to the 'Core Server' profile of the IM Compliance Suite, as HTTP File Upload (XEP-0363) was intentionally left out and only available in the commercial offering, when that's honestly a pretty scammy thing to do since that extension is very essential in XMPP in recent years.

For probably several years now I've been using Prosody which has been very stable and sufficient for a small userbase, but is intended as more of a 'just for fun' project with a focus on very easy moddability, but not architected for clustering (or horizontal scaling).
I took a peek at what the commercial offerings for ejabberd are, and it's pretty much starting 300EUR/month for their SaaS option and that's something that nukes the financial ability of a small community thing just starting out.

Then I was peeking around for other options and saw the mention of MongooseIM in the Pleroma docs, which seemed oddly peculiar given that I haven't seen any endorsement/usage of that software elsewhere. Every fediverse instance I've spotted that hosts XMPP adjacent to their Pleroma/MissKey instance all seem to have opted for Prosody (likely for easy setup, and small userbase), I haven't found much else.

ejabberd seems to be a "open core" mindset (open source base, presumably proprietary extras for the rest of it), while MongooseIM is apparently an ejabberd fork of at least over a decade ago (formerly esl-ejabberd) that appears to be a fully open source offering. I figure that whenever the ejabberd XMPP-Matrix source code drops that people will be able to take some ideas into implementing it into other projects (or just making a portable XMPP component service, for that matter), versus it being an ejabberd exclusive.

Either way, I'm still on a hunt for finding anyone out there that actually uses (or used) MongooseIM and will be looking into it further. I've generally lost all interest in ejabberd. Meanwhile Prosody is still good software for <1k users instances.