It depends on the context. You can't federate with Google, Microsoft, Facebook anyway -- and you won't convert the world to use your favourite new protocol (most likely).
So that just leaves you with an easier problem: how can I host conversations etc for my team/org/my friends? And I think a single, isolated irc server should work fine for that use case, and work fine with many different irc clients?
So no, it's not a universial solution -- I just think it's strange when people bring up slack as somehow "better". Sure it's "better" in that it's a product with backing from some fine people -- but if you wanted a solution based on open standard, Free code that you could self-host without worrying about license costs etc ... then a battle-tested IRC server still seems like a half-decent option?
Or put it a different way: if you have 100s of users, could you get many of the features with IRC, and some bots? (Or maybe a slightly tweaked IRC server etc etc)?
[ed: Not that I claim there aren't problems with IRC -- and I've yet to run a personal ircd, so I don't know a) how much work it is to force TLS+SASL[1] and disable plain IRC, or b) if there are other solutions that might be better, that are available right now.
[1] https://freenode.net/sasl/
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