Your uncertainty about the effeciency of the terrorists plans is really neither here nor there. It certainly does not seem implausible to blow a door off with a shoe bomb and it could occur so quickly passengers would not have time to do anything.
Has FR now gone so wobbly that the cries of 'never again' and vows to follow the example of Flight 93 have completely passed into memory?
I'll be more impressed when I hear of us stopping a plot that someone was actually trying to execute, rather than simply talking about.