In a blockchain-based system, proof of work could give users points so they could spend them to show their trust on a file (or maybe transfer them to whoever they trust so they can release files with a number of points from the start). For the duplication problem, solve it like IPFS does, the file's hash is it's Uri so a duplicate would just point to the same resource. Actually, people could build KAT-like sites entirely in IPFS and users loading (and thus, serving them to other users) said sites would be the trust mechanism.