Lessons of Germanwings

It now seems pretty obvious that the Germanwings air disaster is a classic example of the Law of Unintended Consequences. After the 9/11 highjackings, it was thought paramount to secure cockpits from invasion by possibly bad actor passengers seeking to seize control of commercial aircraft. But that in turn made it nearly impossible to prevent a bad actor pilot from seizing an opportunity to crash a plane. All he had to do was get the other pilot out of the cockpit, lock the door, and crash the plane. In the US, they have the rule of 2, where someone else is supposed to be in the cockpit when one of the pilots leaves, and that probably would've prevented this tragedy. But it seems to me, again, pretty obvious, that a comprehensive review of aircraft control security is in order. What about having an emergency override by Air Traffic Control, that would enable them to take control of an aircraft remotely? (In addition to new protocols to ensure than authorized flight deck crew can get in when they need to).