So much Speculation
Based on the pinging. I've read this whole thread over the days, and haven't commented because I'm not a pilot, just a retired ATC (28years).
I want to say too much weight , in my opinion , is being given to the pinging and radar track(s). A lot of room for misinterpretation of data.
None of the suicide stuff makes any sense. A coordinated takeover is improbable because of what do you do with the acft once you have it? If they're so smart to think of everything, why not just steal a plane off a ramp? It happens a lot. A smaller group of people involved for something like that and they could fly wherever, on legitimate FP and no one would know and they could use it for whatever.
On the tech side, avionics/electronics have been shown to do weird stuff when shorting out or on fire. Humans do odd things when hypoxic, especially if not aware. Confusion, smoke, who knows. I am NOT surprised at ALL that no contact with ATC was made if difficultly arose. You pilots don't do that. In my experience, I never had a ATP tell me about jack until they were way down the decision/action list.
It is natural I guess, but it is a shame this crew are being speculated about on such iffy evidence and extremely doubtful data. The Maylasian Government info is dubious. Too many factors. I think it is possible this one will be unsolved until/unless debri/bodies found. And I lean towards catastrophic inflight incident; fire, decompression, who knows.
Mods; feel free to delete. I just wanted to weigh in.