@jonny I wonder whether uploading every paper to sci-hub twice would be feasible (i.e. would we still have enough people do that). (If we did so, then it would allow sci-hub to verify with reasonable certainty that whatever watermark-removal method they would use still works.)
@robryk
I think it may be easier to scrub it server side, like to have admins clean the PDFs they have. I don't know of any crowdsourced sci-hub-like projects. scrubbing metadata does seem to render the PDFs identical