Not really, I don't see a black market in aviation identitiy cards. The problem is the current situation has killed several hundred passengers and as a security tool is not effective either. The key would be the personal responsibility of the crew member in much the same way that IPads and other equipment is. From what has happened in other events such as Eurowings and MH370 the hijacker is the pilot so a key or whatever mechanism that can allow the other crew member to get back into the cockpit is a step forward not a step back.