Funnily they're doing the same thing with the 737 Maxes undergoing certification now (10 and 7), which have a small design defect in that if the engine de-icing is on and you leave it on after takeoff, it will overheat and melt the cowling... silently, without any warning or sensor or indicator. They plan on fixing this in like 2025 and want an exemption to allow them to certify the 7 and 10, same as the 8 and 9 that are already certified and flying with this defect, with the solution of "pilots should just not forget to turn it off".