System what encrypts content to prevent moderation/censoring and especially distributed systems will very quickly came upon same problems what already broke many other similar systems.
First one is a garbage flood and/or DoS attacks. This will be solved with Proof-Of-Work and/or CAPTCHA things. Posting on such "system" will be slow/painful, but automated floods will be gone. And also some part of community will be also gone because they can't tolerate that complications.
Second one: fat trolls and retards who love to turn everything into feces. They love this because they feel this very "KEK" and they will never stop. Something like Reputation System or Web-Of-Trust will be applied to fix that. And there will be no anonymity anymore. All your posts will be judged to build up your reputation/trust value. This will also scare anons from said system ("trip users" they will cry).
Now we have (for example) PoW+WoT system with pseudonymity. But this system will be skewed in its near future. Because there will be one major group what shares same view on politics/gaming/woman/anime/lisp/etc. And this group will lower trust/reputation of posters they do not like. And if you don't share their thoughts you will be quickly moderated out of the system.
What we will have at the end? Same imageboard with corrupted mods. But this "mods" will not be humans but an artificial algorithm driven by collective unconscious. Is there any difference in being derezzed by .::OneHalf3518::. or by large group of rednecks who believes in Non Flat Earth?
So, moderation is really needed. It's a MUST on an imageboard or everything will turn into a very low quality /b/. And while /b/ is a nice meme and a good weapon for killing time, this is not the main reason which brought imageboards to reality.