> It won’t happen overnight, it will start out as a poor alternative, but slowly growing to become the robust and cheap (in fact, free!) solution that everyone uses.

I'm not sure about that: plenty of people/orgs are okay with using software that someone else will be responsible for running and managing and therefore won't be interested in self-hosted offerings (though one could feasibly argue that there could be managed open source offerings).

In my org, I offered to help with self-hosted Mattermost/Rocket.Chat or another chat solution, since that would allow for a centralized platform for all of the company developers to get in touch and organically self-organize into interest groups, thus easing the friction of communication.

And yet, nobody was interested in setting aside the resources for an instance and getting everyone on board, so the plan never materialized, even though I also run my own instances for personal projects etc. So in the end people stuck around on multiple distributed Skype/Slack/Teams and possibly other chat solutions, it all being a bit too fragmented and sometimes there even being message history limits to deal with.