From the South China Morning Post;
Agree - you won't see debris from 11,000m, but you may see city lights.
Don't think the plane crashed at all. Think it was hijacked by Xinjiang separatists. New flight plan to Hotan airport. Strange that K.L. -> Hotan is exactly the same distance +/- 50km as K.L. -> Beijing. Hijackers' jettisoned fuel to make it look like a crash to direct rescuers to the wrong place.
Classic case of misdirection. They could have easily turned off the transponders, and it being night time, no tracking equipment (from say satellites) would have 'eye's' on the plane.
China's 1st failed hijacking took place at Hotan airport back in 2012. Plenty of opportunity how to resolve what went wrong from hijackers point of view.
In that case the passengers successfully overpowered the hijackers. In this case that might have gone wrong.
Anonymous Pilot mentioned background distress at 1.30am when the Vietnamese ATC asked him to contact the pilots on local frequencies.
Now 4 suspects have been identified (the right number of hijackers required to take over a plane of that size).
(thoughts).