I think people are thinking far too much into this tragedy.
My belief is it was a simple catastrophic event most probably a serious raging fire and the aircraft was pulverised into tiny pieces upon hitting the sea near its original track.
There have been a few instances in history where that has happened where it left very little debris floating.
My problem with the hypoxia then anoxia theory is should the aircraft had headed west over the malay peninsula, crowded airspace with the transponder off then how come no atc controllers on duty in the area noticed it with primary paint and made a song and dance about an unidentified aircraft being in their airspace. Sure a military facility claims they painted the aircraft but that is not officially released info. If the military painted it then so would the civvies.
I believe this current preoccupation with engine or airframe reporting picked up by inmarsat may again be over-reaching. Are inmarsat absolutely 100% sure they were listening to the accident aircraft? How do they know MAS hasnt been swapping systems on the planes for maintenance and the system registered to mh370 was not on another plane?
As for the terrorism angle, excepting 9/11, most terrorists want to announce to the world what they are trying to achieve, not cloak and dagger so turning off transponders etc... Achieves what advantage for them?
The vast majority of accident sequences end up being very simple indeed. Anything else requires complexity that is outside the limits of most people.