I don't think IRC went away. More like IRC was an old crusty alcoholic down on its luck, Ms. XMPP (once a cool chick) was having a need-a-pregnancy crisis in middle age, so went to a sperm bank, made some bad jokes about plugins, and wound up getting pregnant. Shortly after that, XMPP met a VC who thought the child was its own. Thus we have the test tube baby called Slack, who takes after its father in capitalist tendencies, and mother in pragmatism.