I think that depressurization is the reason for the plane's disappearance. I think I read somewhere it was reported a few years ago that the 777s were developing cracks that could result in a loss of cabin pressure and the planes needed to be inspected for it. I think they all died of hypoxia, pilots included. Like Payne Stewart's Lear Jet, it finally ran out of fuel and fell from the sky. The question is where did it fall?
But the hijacking scenario is still interesting. I would think they would want the plane for ransom and not to use as a weapon, though.
The only problem I have with accepting your explanation is that MH370 drastically changed its course 12 minutes before the pilot signed off with "goodnight" to the Malaysian ATC. Given that there was no sign of any distress at the times leading up to, during and for 12 minutes after the drastic and conscious change in its scheduled direction, the only logical deduction is that MH370's pilot(s) had "other plans" for the aircraft. The added fact that MH370's new course perfectly intercepted the Berlin-bound IL68 (also a Boeing 777) makes a strong case for MH370 having shadowed IL68 across the Asian mainland to its alternate destination.
LtGen McInerney is a very knowledgable authority, and I would not discount his experienced opinion.