While a list does sound like it could be useful, one of the issues I see with it is that it would have to be updated for every single MOTS event. The reason for this is that while someone might not want to say, participate in the Spring MOTS because of other commitments, they might want to be eligible for the Summer MOTS.
That said, this idea does have some merit, especially if there was the possibility of a self-editing list from which people can add and remove their own usernames. Might be worth exploring that idea further.