Don't allow users to rate/add to "watched" movies that haven't even come out yet.
Movies like the 2017 Star Wars one. No one on Letterboxd has seen it, it's not even finished, they are filming it now and it's just annoying with people marking it as "watched" and giving out high grades to it.
This would also be great if there was a way to do this for older films that are considered lost. There are movies on the site that no one has seen since the 1920s, yet they have ratings and even reviews.