This is really interesting, I do not really see any problems with the current implementation. Although this will require very profound changes to all the frond ends to the point that it may be faster to just recreate one from scratch using components from the old ones.
I tend to disagree on the "mutes are not retroactive" part.
mutepost operations.In terms of features that are "nice to have" would be the ability to set your own ads. This way communities can run things where they share ad revenues to their best authors and are incentivized to break the echo chamber and share their page to the outside world for more pageview. They get ad revenue and the frond end earns backlinks, it's a win/win
RE: Feedback Wanted: “Communities” Design Document