IRC with good mobile/push support could have taken off, but using it from a mobile device is painful because of the constant drops and the need to have your device responding to ping pongs every few seconds kills your battery.
You mean, something like IRCCloud, or what I’m moving Quasseldroid to right now?
"Something like irc cloud" should have been baked into the ircd/protocol so that there's a lower barrier to entry.
The push notification systems used by Android and iOS only allow the same person that can authorize updates for an app to send push notifications to this app.
This means either every IRC app would need to operate an open gateway for notifications, or you’d need to give every IRC server the same certificate that you use to sign your app updates on the Apple AppStore.
Push notifications on mobile devices are designed to only work for situations where the same company controls all servers, and apps.
Things like this are the reason slack and discord ate irc.
Most users simply won't sign up for 3 services just to chat.
The protocol between the quassel core and clients looked to be some sort of serialized Qt objects (iirc), so I abandoned that idea and wrote the irc client backend in erlang, with a json protocol.
It's planned to be replaced it with protobuf relatively soon, though.