Earlier quoted context omitted.
I never really understood why Matrix invented their own thing instead of building on an already existing IETF Internet Protocol. Surely an "eventually consistent database" can be built on top of XMPP? It's just message passing. When evaluating WhatsApp alternatives, this somewhat made me choose XMPP over Matrix. I recently uninstalled WhatsApp, Telegram and LINE (felt pretty good) and now use Conversations with most…
It's a fundamentally different approach. You could in theory build it on top of XMPP, but it wouldn't actually interoperate sensibly, so what's the point?
Is it? (genuinely curious) Can't one see the matrix server-server state synchronization protocol as a transport layer for MAM archives? And pubsub nodes in XMPP are very matrix-room-like. This could be an XMPP extension allowing to multi-home pubsub nodes.
Also, there are recent matrix proposals [*] for representing several things (groups and user profiles) as rooms. Given the analogy room=pubsub, the user-profile-as-room seems to be the same thing as XMPP's PEP (used to share personal data, like public keys or avatar). And the group-as-room would be the MIX proposal.
[*] https://github.com/matrix-org/matrix-doc/blob/matthew/msc177...