Yep. I agree with this idea. I think although corn brings up the point of having to update it every month which is a fair point, the work it takes to get checkmark far outweighs the effort to update the board once a month. I don't really have a lot of knowledge about this but could it not just be automatically updated like the leaderboards are? If so, I don't see the drawback of having the board.
Another idea instead of this is just making a leaderboard for the unique map completions which pretty much serves the same purpose and also includes players who are very close to checkmark. Although this could pose problems if more than a certain amount of people get checkmark cause it would defeat the purpose of everyone's name showing up who has the checkmark. I don't know, just something to consider.