One of the things I really appreciate about IRC is the raw simplicity of the protocol. I hope that does not get lost in an effort to modernize.
My opinion is that a strong 'minimum' protocol is critical to interoperability and opportunities for federated protocols to function well across providers. I recall that was the main, non XML, reason that XMPP failed. Of course I also dislike XML as a data storage / transmission format.
And it makes sense, IRC is already out there and has a ton of servers and clients working, you can't split that community based on the client they're using otherwise you're just creating yet another isolated chat protocol like a ton others before it.
I think the point is that writing anything for anything is simpler, faster, and has fewer dependencies when parsing is easy.
> Also, Matrix uses an HTTP API and almost every language at least has a binding to libcurl.
Certainly there are advantages of using Matrix and it's HTTP compatibility to implement some solutions. However, I can also imagine some projects are best served with a simple protocol with lean libraries that don't incur unnecessary dependencies on HTTP and the related bloat and complexity.
That's basically everything you need to know for some basic chat.