I didn't say you should; rather, my point is that the problems with IRC mostly happen at the client level rather than the protocol level. Of course, it is also hard to ensure that a dominant client vendor does not start trying to add backwards-incompatible changes to the protocol. This has already happened once, and it's why the character U+0001 is now responsible for /me.

I think ideally such a client could be implemented as a plugin to an extensible terminal emulator, which might help to keep the project small and prevent Jabberification.

Something like Quassel had most of this functionality more than 5 years ago, while looking at least as good as Slack. I haven't used it in a long time but I'm pretty sure the setup was simple (not one click, but certainly easier than tmux, etc). It's a Qt app, so might be a better fit for non-technical users.