I wish we can scale your example.
Back to the topic. I guess nobody objects against self-hosted alternatives if there are people willing to take over the maintenance and having some backup and the mechanism of passing the baton. The missing part right now is a collection of links showing where SustainOSS is using non open source technology. As far as I know Discourse is FOSS, and I can don’t remember where Slack or Read The Docs are used, even if RTD is open source while GitHub isn’t.
What I would like to ultimately see, though, are metrics about time and expertise needed to maintain those hosted solutions. People need to know what it takes to maintain community infrastructure to be able to support people behind it.