On the subject of IRC: it wasn't fading all that strongly, IMO, at least for open-source and free software discussions. Then Slack came along. Startling to see a proprietary clone of IRC (albeit with some nice extra features, namely history) come along and start taking over. See, e.g., the Clojurians Slack community.
It's also got basic wiki type stuff, and some other features.
IRC is like USENET: It has barely evolved for decades, nobody can profit by improving the protocol as it's a commons, so it just stagnates and dies out.
Eventually all the decentralised protocols that were born in the early days of the internet will be gone.
The IRC protocol is in a different situation to USENET, because the latter has many different independent, individually federated networks of servers, whereas the latter has just one.
This means that server-side innovations can and do happen - they just need to respect the basic server-client protocol. Often the newer features are delivered through "services", which means they're in-band signalled.
Not entirely. Team control is a major part of it for companies, and history makes a huge difference to the experience. Slack servers allow the use of IRC clients, but I gave up on Colloquy almost immediately after seeing the benefits of history. For the right teams, the IRC+history combo can almost completely eliminate email use.
Also, Slack bought a company which did voice, video, and screen sharing. Since join.me went downhill, this will be a welcome addition to Slack.
