they made the cockpit doors strong because of 9/11. And then the co pilot was able to get away with this mass murder because of a 'safety' upgrade.
Law of unintended consequences is how they will try and spin it; what it really is just typical bureaucratic BS where something is not thought thru just knee jerked to appease the mediots whining and crying.
If you are going to make the cockpit door a barricade then you need carefully thought out procedures to try and prevent what happened on that flight. To begin with there should NEVER be only one person in the cockpit.
and if they are going to make all aircraft now computer controlled then they should have a way to hit the panic button so that the computer takes over and lands the plane safely. BUT THAT needs to be carefully thought over as well. They can do things that will cut down the odds of this happening again but I am not confident they are smart enough to do it right.