I think the community subscription model in the article fixes this (imperfectly). Pancakepurists@a.com can have strict rules while pancakeparty@b.com could subscribe to it and pancakepurists could subscribe back with the understanding that the rules are slightly different there. Pancakechaos@nazi.assholes could similarly link to both those without either having to be mutually interactive.

I think the problem comes from some increased moderation loads by allowing a community to follow another. If I were to put on my paranoid hat it could be used to monitor and brigade a community. I think the solution for that is moderation tools. Banning instances, federation etc. I'm not a mod anywhere so I don't know what is possible.