Most of how I use Slack, and how everyone I know uses Slack, involves 1. sending messages to people who are “away” to get their attention/loop them into a conversation; and 2. people reading back up in history for context when they come online.

Now, modern IRCds might have features I’ve never experienced on raw IRC... but if they don’t, I don’t suppose you’re suggesting that this server also run thousands of bouncer bots in order to provide this contextual history feature?

(Also, whence push notifications?)