If some physical evidence in the local area doesn't turn up soon, then we will probably have to invoke Sir Arthur Conan Doyle's hero, Sherlock Holmes;-“Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth.”
With all the myriad possibilities, has anyone considered the recent EY461 incident ? I doubt that would cause a sudden disintegration, but it is a recent event, and originated in that part of the world.
Did 9M-MRO have inflight wifi service ? Another method of getting something out, if there were sufficient time to do so.
From what various posters have said, the aircraft was not under civilian primary radar coverage at the time the various signals were lost. If there had been a naval ship in the area, with an air search radar operating, they may have seen something that could lend a clue. Beyond that, if the aircraft ended up transiting some remote land area, would a military radar automatically scramble jets to see what was up there, or would they note it and ignore it (because it wasn't considered a threat) ?