The sad thing is that the most constructive post 9/11 change they made, is just to reinforce the cockpit doors and change some of the procedures for when a pilot comes out to use the restroom (a flight attendant will typically block the way as he does that, sometimes with a cart, to make it hard for people to run up at that moment.) That small set of changes was cheap and safe with basically no downsides. Everything else is an expensive mess.