Earlier quoted context omitted.
Actually that makes a lot of sense, it's not that we need to have RSS replace Facebook, we need a resurgance of forums to take back from Facebook. Perhaps if forums could talk to each other you'd have an experience more like mastodon, but in concepts that more people understand. Something like an open source Stack Exchange network. So you can log-in to one of them but then easily create an account using the credentia…
Sounds like subreddits.
Each forum could still have their own domain and installation.
Ideally it would be in some way compatible to existing forums.
Perhaps better integration of forums via RSS. One thing regular forums tend to still have is RSS feeds built in. They can also be a nice go between of email and online users (although as has been said many times, email an be the death of forums).