>>feross+(OP)
I'm not sure I buy that the MVP here is actually "viable". Suppose you're Reddit, and you have FatPeopleHate on your site, and you "ban" it, in the sense that you hide it from users who have not opted-in. Does that really provide the same level of enforcement as a true ban? It seems to me that the presence of that community on your site has effects that spread beyond the community itself, it shapes the way people interact even outside the soft-banned subreddit.
I'd be willing to bet that if you could somehow run an experiment in parallel where you had one Reddit with real bans, and one with soft bans, the quality and nature of interactions on the soft ban one would be much, much worse even outside of banned communities.