Changing the rules isn't going to do anything to save the class other than split the fleet into stock and aftermarket sails groups. What is gained when 5 Nacra 20's show up to an event and 3 of them have stock sails and 2 of them have aftermarket sails? It does nothing but dilute and divide the fleet.
If you want open sails then go to a class that allows open sails. Don't change the rules after people are already invested in the class.
Since most sails have a competitive lifetime of about three years or less, designate a transitional time period? During the transition is the tough question.