You can have zap to see content, or subscription only content, or anything else that's relay- or client-based, but I don't see how you could avoid being identified and caught if the content itself is illegal in the jurisdiction where you operate.

I'm not trying to be a black cloud, just trying to break the problem down to manageable solvable specific issues because it's not clear to me that we have a full picture of the needs, or that all of the needs can actually be solved at all. 

 One thing I do say all the time is that relays should be absolutely dumb, to the point that in my opinion content should be by default ephemeral: if a user wants to store stuff, they should do it using their own hardware.