'Eliminate all other factors, and the one which remains must be the truth.'
MH370 has not been found anywhere near it's last established position because it is not there.
It has not been found anywhere else searched because it is not there either.
It was not hijacked and there is no conspiracy.
There was no devious plot with the crew using a sim.
There was no systems wide instrument failure.
It did not disintegrate at FL350 or any other level
It was not crashed into the sea or a mountain or secretely landed on a well hidden strip on some remote island.
Aliens did not abduct the plane, crew and pax for some odd experiement.
Vietnam, Laos or any other country did not shoot it down by mistake as part of a new secret weapon test that went wrong.
Perhaps the crew and pax went hypoxic but if a planned track west from IGARI WP to VAMPI and multiple others as has been suggested westward then it was hypoxia with intent and a plan.
So what if the crew just went dark, turned around and made a track west? You would need a complicit cabin crew and pax for 5+ hours to carry that off. You would need both pilots "in on it". And then there is the motive. In the absence of evidence at this time perhaps that is simply what happened and they ended up very far west deep into the Indian Ocean and ended up in the drink.
So the question to ask if such could be possible is what would the flight deck, crew and pax of a servicable aircaft all have to have in common for that whole idea to be viable? Something aboard (no conspiracy of kryptonite) that secreted into the environment aboard and rather like something hallucinogenic simply gives rise to a different level of behaviour? Something that does not alert the pax or crew to any deviation from the flight and for the flight deck to go dark and make a deliberate track west without any malice. It's the hypoxia theory that works in practice with the circumstantial evidence to hand. As has been suggested here, the manifest is one thing but what else was aboard? It does not need to be something of malice just something(s) that in the right set of conditions combine to give "operational paranoid hypoxia". Something that incapacitates the judgement of all souls on board hence no panic to make cell calls or other raising of alarm or trying to take the plane back or anything else for that matter. It just went west in a complict way without malice or plan and ended up down somewhere very far from where SAR assets have been looking.
Well Sherlock Holmes would probably have a mind to consider something of the like...