Another massive hole is that the closest airport ,at the point where communication was lost, was Sultan Mahmud in Kuala Terengganu. Long runway, approach directly from sea, can accommodate a 747 according to Wikipedia. There is no justification to go to Langkawi which is on the other side of the Malay Peninsula.
Never underestimate "pilot familiarity." In an emergency, a pilot is going to favor an airstrip he/she is familiar with over an unknown one. Perhaps the captain was more familiar with Langkawi?
In an emergency, the safest way to burn fuel is to reach the closest airport and then circle it. Not head to a more distant airport which you might not reach because of the very emergency.
All hypotheses will invalidate the major premise: that the pilots chose that particular heading not randomly, but in a calculated attempt to reach the nearest airport because of an emergency. Basically, no matter where the plane would have turned, if you draw a long enough line you will find an airport. But that does not explain anything.
