"Lets not forget that the SLF overwhelmed a well organised team of box-cutter armed hijackers aboard UA 93"
Yes, and the passengers and crew died. Certainly they stopped the aircraft from being used as a weapon, my goal is to never let them in the cockpit to begin with and try and save the lives of those onboard. Sorry, UA 93 was inspirational, but it wasn't any type of success for those onboard.
"With the current doors, the hijackers face great difficulty gaining control of the cockpit before the SLF get to them"
I don't mean to be demeaning, but what is your experience with the door? Its my experience as an airline pilot who deals with the re-enforced door that you are putting much stock in something that is but one part of a layered defense. It is not the end all.
Heard of the maginot line?
"before the SLF get to them"
What if the SLF are being mowed down by a weapon? The doors are bullet proof for a reason, that being the possibility that weapons can make it on board. You want to be the third SLF that runs forward when the previous two are gutted by the attackers? Perhaps you will, or worse perhaps you won't. I'm not prepared to rely on the sketchy, unpredictable human responses as a viable deterrent or solution.