Earlier quoted context omitted.
Except for message retention and search, IRC already has all that, and even that is possible with bouncers. Mobile applications with notifications, conversation threads with +draft/reply (IRCv3 draft), multimedia attachments (IRCv3 idea), authentication with SASL and standardized account management (IRCv3 draft), etc. Look at what IRCCloud provides, and what IRCv3 is doing.
> Except for ##2 killer features##, IRC already has all that, and even that is possible ##if you implement it yourself##. That's what normal people see when they read your message.
Even if you want to self-host, there are solutions — get any server, run
docker run \
-v /path/to/folder/where/you/want/to/store/the/config:/config \
k8r.eu/justjanne/quassel-docker:v0.13.1
and connect with quassel or quasseldroid to that server (the setup wizard guides you through everything else). It's about as simple as it can get for selfhosted. (Quassel gets you message retention and search immediately, and the other features are already being worked on).