Hmmm. Good points. Maybe you could somehow turn that into an intended feature. I am not sure how this could be done (a crude idea below) but the idea would be that only those currently in the community could see the post. Individuals added to the community at a later date would not have access to posts created before their acceptance into the community or afterward.

The crude idea (very crude as I am not a coder) is when an encrypted post is created the key to that post is broadcast to a whitelist all current community members. Every post would have a unique encryption and whitelist pair. That would get complicated but I guess it could be offset with high RC costs if it is resource intensive.

Anyway, thanks for entertaining my ideas. I will let you get back to work on more productive things. Cheers.