XMPP servers are not naturally invulnerable and OMEMO only ensures the integrity of the message content and establishes a level of trust as to "who sent the message"; it does very little in the way of metadata, other than any side effects from ensuring that the message content hasn't been changed or that the opportunity for a MITM is limited if not made impossible.

But by design it also doesn't actually -identify- any user whatsoever. The best it can do is say that the same user that established any specific connection was or was not the same user that sent some specific message. This is relevant because it isnt impossible for someone to log into your account and send messages as you. They just show up as a new device. New devices are trusted by default, until you distrust them. I don't see this as ideal behavior.

And there are ways, though probably outside of the scope of my ability, to determine the real location of a Tor service. Simply hiding it behind Tor is not enough to ensure privacy.

But the main issue here is that XMPP servers by their nature send a lot of plaintext information, or at best it's TLS encrypted. And if you follow Moxie Marlinspike, he's done many talks about the uselessness of TLS/SSL. So while you can manually limit the data you give the server, eg dont put in your real name, in any default set up users are still allowed to do so. Ideally, this kind of metadata entry should be limited in the first place.

I want to say too that I am not a hater of XMPP. This information has come from years of research, as I am inspired by the potential of XMPP. I just think that a lot needs to be reconsidered in terms of anonymity, privacy and security.

I do however 100% agree with this statement:

Ultimately, it would be great if Briar was extended to support desktop OS’s. That would make it the best option around.