You can't build a modern messenger equivalent on IRC. You need a new protocol.

"New" is relative of course, XMPP is 27 years old. Still, XMPP lacks official support for something as basic as "I want to log in on a new device and see the old, encrypted messages that are on my other devices".

IRC itself is a reinvention of `talk` and BBSware. For as long as there will be new use cases, there will be new protocols.