A rule like that would, I believe, be detrimental overall. People generally only want to participate in a tournament for a bit of fun - they don't want to waste time acquainting themselves with the community. The 30-post rule is guilty for stepping on these people too, but the proposed rule would do so even more.
Here's an alternative I suggested in Chat, which could potentially replace the 30-post rule: reinstalling Quizzes and forcing everyone to complete a quiz on tourney rules before they can participate. This is quick, easy, and ensures that people read the rules. I understand that this was suggested before and possibly used, though my memory fails me. One of the reasons against this was that it did nothing to prevent cheaters using multiple accounts. I believe that this was before the new chatroom where all mods could see IP addresses was installed, so this may not be such a problem any more.