[zajio1am]

XMPP had rather bad name. Well-known design issues causing message losses, fractioned ecosystem due to varying implementation of extensions, unsuitability for mobile clients, absence of synchronization between clients, absence of end-to-end encryption. Most of these issues were (much) later fixed by extensions, but Matrix (or Signal for those who do not require federated one) was already there, offering E2EE by default.

Even today, E2EE in XMPP is rather inconvenient compared to Matrix due to absence of chain-of-trust in key management.

[zadikian]

Sometimes I wonder if the endgame is each person having their own XMPP server for their set of devices. S2S is your E2EE then. Your chain of trust is your existing CA, unlike Matrix which starts from scratch. Cause XMPP wasn't designed from the start for clients not to trust servers, plus the fragmentation of C2S extensions was always a pain.

It's not a bad solution if someone can make it easy, even if it's a managed service that just lets tech-savvy users export it to self-hosting if they want.