IRCv3 has "chathistory" extension. It basically involves combining an IRC network and a bouncer. There are at least two server implementations using it: ergo, which is more or less production ready, but does not have support for multi-server networks, and Libera's sable, which is under (very slow) development.
I wonder why such thing wasn't done 15...20 years ago. Now it seems to be too little too late, with Matrix more or less having been taken the place of IRC.
I guess that because of the "we don't need that here" attitude that ran a lot through the first generation(s) of Internet population.
And it's a shame because with a more dynamic IRC development we wouldn't be in the Slack/Discord silos situation.
Or maybe we would have been anyway because adding more and more complex features to federated, open-protocol systems with many actors involved with different, maybe even competing interests is not easy at all.
But also if I think back at late '90s, IRC had almost the needed critical mass and non-tech users to become something more mainstream...
I wonder why such thing wasn't done 15...20 years ago. Now it seems to be too little too late, with Matrix more or less having been taken the place of IRC.