@wilhelm I've been thinking about it some more, and I think we should reuse some of the existing behavior (no access to public profile pages like photos, posts, calendar, etc...) but replace the access permission currently granted to authenticated users on the same node (and magic authenticated visitors) by the mutuals check.

Interactions would be:
- Displaying (Web UI)/Fetching (Protocol) posts/photos/events, both in list and single form.
- Searching posts.
- Liking/Disliking posts.
- Comment on posts.
- Direct mentions.
- Private messages.

Of course the description of the setting should e way more verbose to explain all the effects of it.