Passing legislation for a one off case is always a bad idea.
I followed the aftermath of this case for other reasons, and frankly unless you wear a tatoo saying " I am an airline pilot" to warn the Psychiatrists of the MD who you really are, and then you will need to force Medical doctors to warn your employer that you are unfit to fly, it will not work ,there is little you can do to prevent this in our open societies.
Lubitz went to see over 20 different doctors , was reported unfit to work by nearly all of them, but only a few declared they knew he was a pilot, and those one who knew just gave him a paper to stay at home.
EASA legislation will not change this.
Only in Russia (and some other CIS states ) I believe Airline Pilots are still given a medical check before every flight, by a company doctor. Was at least still like this a few years ago. Good lefts over from the Soviet times.
Last being 2 or 3 or even 4 in a cockpit , will probably not prevent a highly intelligent psychopath to hide , and do what he wants to do. That is at least what all the psychiatrist say.