2. Server can store messages to catch you up when you return
Personally I feel Matrix is the right way forward for most use cases but Matrix will continue to bridge to IRC so you have options. IRC remains a much easier to implement protocol and much easier to deploy for standalone environments where federation is not needed.
There is a reason most infra teams at FAANG companies keep IRC servers around as a fallback for when their complex proprietary solutions fail.
Matrix has a lot of nasty issues, I'd argue XMPP is probably the right way forward for small group chats and one to one convos. I personally refuse to use matrix since I still don't feel comfortable self hosting it.
For large group chats IRC is still king.
EDIT:
There's pretty much one useful server last time I checked and it's too bloated to host in most places and it looks to me like this might be at least partly due to the way federation works. One of the main organizations funding Matrix is that one company in Israel that was contracted to do all the phone surveillance in the US. I haven't really been impressed with the protocol itself either.
In short, I don't think Matrix will "mature" since it's problems are deeper than just technical/implementation. XMPP already is mature and there are good clients and servers for nearly every platform.
IMO: The only reason Matrix is more popular than XMPP right now is just PR.
Matrix has really interesting properties for censorship circumvention, but their approach has drawbacks: designing an append-only log with consensus building takes a lot of resources (though the implementations are getting better). It's not uncommon for medium server operators to report >10GB RAM usage and at least twice as much database storage... which is quite too much for most of us.
Also worth noting, there are also issues regarding the fast evolving protocol. Room protocol versions keep increasing and if some server doesn't have the very latest version it may be unable to federate with a more modern room, from what i understand. (please correct me if i got this wrong)
Finally, some pseudonymous persons are really unhappy that as a consequence of decentralized rooms, your public matrix address is leaked to any server federated with a room you joined. Under IRC, addresses are local to a server (not federated) so this concern does not apply, while on XMPP only the servers/services you explicitly connect to know of your JID.
In the meantime, IRC and XMPP provide useful services with 1-10% of those resources, despite most clients being less polished. For example, jabberfr.org uses only a few gigs of RAM for hundreds of clients and over a thousand of server-to-server connections. Not all features may be available on all clients/servers, but "graceful degradation" is definitely there so noone is left out.
To be clear, decentralized room is an amazing concept, and it's really cool the Matrix team has full-time employees to evolve things that quickly. It's just too bad historical standards were left out (decentralized rooms could have been a XMPP extension), and Matrix focuses (though this focus is changing) on high-end clients/servers.
How is the compatibility with federation and clients? Any issues? Last synapse upgrade half of my clients just stopped working due to some incompatibility between the newer synapse server and a too old shared library (that all the desktop clients used).
I've used web, android and desktop clients without problems, other than the android notifications. I'm using it as a private chat server; I haven't tried out federation since I was setting it up. I can't see an issue on the bug tracker though.
Does it support gateways properly? I'm still interested to give it a try but last time i checked Bifrost was not compatible with conduit.
Also, how's your database RAM/disk usage? From what i understand conduit.rs is very optimized but still relies on a huge DB for matrix to operate its magic.
XMPP is a nonstarter -- there is no decent free iOS client, unless there's something new that has appeared in the last few months with a lot of features
Some people prefer to chat on desktop and don't really like the mobile-derived UI and prefer a text-heavy dense layout.
Throw in lightweight resource usage as a requirement and suddenly there are not that many working alternatives anymore.
Two of the most major changes:
1. First-class mobile-friendly websocket support.
2. Server can store messages to catch you up when you return
Personally I feel Matrix is the right way forward for most use cases but Matrix will continue to bridge to IRC so you have options. IRC remains a much easier to implement protocol and much easier to deploy for standalone environments where federation is not needed.
There is a reason most infra teams at FAANG companies keep IRC servers around as a fallback for when their complex proprietary solutions fail.