> IRC is complete trash and I don't know why anyone would use it in the same sentence as Slack. UX matters. It matters A LOT.

To me, that sounds exactly like someone defending AppleTalk, AOL, ICQ, or Minitel. Focus on usability, not interoperability. That's what people want, right?

When it comes to communications, what matters even more than user experience, in the long run, is being compatible with everyone, even your competitors. There will always be customers who don't use your system, so lacking compatibility or federation will be a thorn in your side for as long as you exist. I've run out of fingers to count the incompatible proprietary chat systems I've seen die off.

Even Google has killed off a few of their own, and Hangouts is next. Just being a young smart agile tech company does not make you immune.

In 10 years, I bet people will be communicating over email, IRC, POTS/SMS, plus 4 or 5 new tech startups created by people who are in elementary school right now. Nobody's arguing that $(proprietary_system) doesn't make you more productive today (that's the point!), but they always have a sell-by date.