Earlier quoted context omitted.
I don't think this is the future of the web. This sort of thing is a temporary blip before everybody figures out decentralised solutions for everything. Decentralisation is clearly the end game as long as politics causes problems like this. A decentralised solution will continue to "just work", while centralised solutions continue to boot people off. It's pretty obvious which one is going to win.
Except looking at the past 20 years or so it seems clear that the trend is going the other way around. Slack itself is an example of that, not long ago it would've been a set of self-hosted tools. People have ditched IRC in favor of Discord and friends, they've ditched decentralized forums, BBSs and mailing lists for social networks, everybody hosts everything using the same four or five cloud providers, streaming an…
Regarding your note on the path of least resistance leading to centralized solutions---Glowing Bear/WeeChat is definitely more work to set up than just signing up for Slack. You need a machine that runs WeeChat and get a TLS certificate so that the browser will let you connect securely. That definitely limits it to a somewhat nerdy demographic, even among the HN readers ;)