You sound the most plausible, because I think some satellite or radar would have picked up the plane, if it made it to Pakistan or one of the countries they are talking about.
The pilot seemed to be the most suspect, if it was a hijacked plane, but that does not mean the co pilot was in compliance....crashing makes more sense, even if he tried to hi jack.
The most crucial things - aside from the plane itself - that need to be flight are the Flight Data Recorder and the Cockpit Voice Recorder.
Provided they survived, that should pretty much reveal everything. In the meantime, sure.....it’s fun to speculate. Everyone loves a mystery; as a famous fictional detective once put it, it’s good for “the little grey cells”.