The "hijack theme" of breaking into the cockpit and wrestling control from the pilots is no longer an option for terrorists. This technique has already been expended and would no longer provide an element of surprise.
The knowledge and certainty that all concerned passengers, fearing for their own safety and survival, would pounce on any prospective hijacker(s) makes the likelihood of this scenario and the necessity of pistol packing pilots history. (El Al pilots are unarmed).
As has been demonstrated in the Middle East, the greater danger will come from suicidal martyrs with explosives strapped to their bodies. Getting past airport security checkpoints with undetected explosives on body or in checked baggage must be the mission of enhanced airline/airport security.
Additionally, airport perimeters could be made more secure. Instead of an ordinary chain link fence, a concrete retainer wall encompassing terminals and runways would prevent potential "truck bombs" from being driven and crashed into taxiing jets.