What are your feelings about people being able to make 'revisions' of their own work - this is standard in regular publishing - 2nd and 3rd editions in which you want to keep 80-90% the same but just update.
As far as I'm aware you can't do that on here without being caught by your bot! This could be problem for anyone who specializes in very narrow fields, and might legitimately want to re-post a refined and improved version of something a few years after the original, which is similar, yet better.
As you say, cutting down on plagiarism is a tough one, but thanks for the efforts!