Where I work, before Slack, we had Campfire and only us developers bothered to sign up for it, get the client, etc. We switched to Slack and suddenly everyone was on it. UX matters so much. We don't have time to tend an IRC server and act as support for it. Slack lets the whole company sign up ultra-easily and get on board – there's simply no contest.
I lament the passing of the age of new open protocols too, trust me, I really do. But IRC+ecosystem just isn't that good these days, and getting stuff done matters more.
I lament the passing of the age of new open protocols too, trust me, I really do. But IRC+ecosystem just isn't that good these days, and getting stuff done matters more.