I think Occam’s Razor points to no conspiracy, but simply another singleton example of Sudden Jihad Syndrome a la Egypt Air, but with a destination and a target, thwarted by the pax and on-board engineer.
This would be very problematic, P.R.-wise, for a struggling national airline with mainly muslim pilots. Even worse than a mystery helped by national incompetence at tracking airliners.
I do agree with your assessment of Sudden Jihad.
It’s simplicity is its strength, and by far is the most reasonable explanation via Occam.
The “to be used later” and even the Diego Garcia angle involves a conspiracy far greater than can be contained by a few individuals.