Earlier quoted context omitted.
This doesn't resolve the multifarious issues with identity, reliability, scalability, federation, standardisation &c &c that further rule IRC out from being the universal panacea.
It doesn't have to be. Go help with IRCv3 - http://ircv3.net/ . Almost everything that's in Slack and Zulip would just be a capability extension.
My interest is in federated, reliable, ad-hoc messaging and IRC's acyclic forwarding graph and lack of any inherent identity model make that impossible.