A Startlingly Simple Theory About the Missing Malaysia Airlines Jet
The best theory: an onboard electrical fire and a captain aiming for the nearest, safest runway.
There are two types of fires. An electrical fire might not be as fast and furious, and there may or may not be incapacitating smoke. However there is the possibility, given the timeline, that there was an overheat on one of the front landing gear tires, it blew on takeoff and started slowly burning. Yes, this happens with underinflated tires. Remember: Heavy plane, hot night, sea level, long-run takeoff. There was a well known accident in Nigeria of a DC8 that had a landing gear fire on takeoff. Once going, a tire fire would produce horrific, incapacitating smoke. Yes, pilots have access to oxygen masks, but this is a no-no with fire. Most have access to a smoke hood with a filter, but this will last only a few minutes depending on the smoke level. (I used to carry one in my flight bag, and I still carry one in my briefcase when I fly.)
What I think happened is the flight crew was overcome by smoke and the plane continued on the heading, probably on George (autopilot), until it ran out of fuel or the fire destroyed the control surfaces and it crashed. You will find it along that route–looking elsewhere is pointless.