The issue with megathreads is that they're beholden to the whims of the original poster. We have absolutely seen cases where a poster is willing to tweak the original post to edit in new relevant requests/references to what has been asked for by people responding to the thread in good faith.

Unfortunately we have also had original posters who, for example, decided to deliberately hide away certain requests and references behind a spoiler box in order to promote only those that they themselves desired. With no real attempt made to compromise.