The copies would need to be encrypted kind of like freenet style, and it decrypts as you log in.. the passes could be hashes that check in the blockchain so it's like keeping your private keys from bitcoin safe... just throwing in some ideas.
It could probably be done but im not a good enough coder to actually get it working. I would wait until we have sidechains, I don't really see people throwing in electricity for a PoW that only servers this forum, we need to take advantage of the BTC blockchain hashrate.
Too complicated so for now we'll have to deal with the ddosers the oldschool way.
I could probably do quite a bit of the signatures stuff. The transmission would be what I struggle with though but that could already be sampled from the regular core.
As for the proof of work, that would be done whn you post, each post is a block and y'all get the score (or it could even be each topic is a block, you download the block, sign your new block, verify the entire block after checking the signatures of all the transactions/posts inside of that block/thread)...
Interesting take on it, but im not sure about post per block, even thread per block, I mean, as with everything in life, it is prone to exploits, in this case people could just spam the fuck out of it, I mean this forum is pretty fast paced already, so I have my doubts this would work out well. Perhaps more advanced members would have their "blocks" mined with a priority.. merit could act as a "fee" of sorts? im not sure, there are some good angles to research in the field of decentralizing a forum and protecting it against ddos. But then, if it becomes too complicated for noobs to get started and posting, someone else may just attack the niche with a classic forum and get traffic away from deflecting users of this forum in current form, ranking better in Google and then ending in ad revenue loss... very hard to balance things out here.