One other feature that's absolutely considered table stakes now is persistent server-side history, with the ability to edit and delete messages. Modern chat services are less like IRC, and more like a web forum with live updates.
(Yes, you can poorly emulate server-side history on IRC with a bouncer. That's not enough, and it's a pain for users to set up.)
In fact this is the reason some irc networks blocked matrix bridges at first (they now have settings to disable this)
I'm not saying mainstream people should use IRC though. Matrix is better for that.
Telegram lets group admins choose whether members can see history from before they join, which is the perfect solution (IMO).
Indeed.
Ergo offers server-side history but I'm not sure it supports edit/delete yet.