A very large UFO flown by aliens is my first guess. I suppose I should be used to this by now but having so many conflicting so called facts floated about willy nilly is not helping the cause.
Some of these systems should not be able to be turned off from inside the aircraft. The FDR and CVR should run regardless and their information will be on the fluorescent orange boxes aka black boxes. Of course, they need to be found first. The transponders and ACRS can be disabled from inside the aircraft.
in addition to the wild speculation in the so called main stream media there is even wilder speculation in the industry media. One account has co-conspirators of the co-pilot aka SIC, using a garrote on the captain while the others disable the O2 system with the aircraft depressurizing, killing all pax, then descending to near seal level where they dump the bodies over board. Then they fly to a remote landing strip, load an atomic device and drop it on Israel. All nonsense.
The aircraft did have enough fuel to fly another 2000+ NM IF it stayed at altitude. Being at altitude allows all sorts of radars to see you, especially military radars which will not necessarily be looking for transponders. The best bet is to fly low to get under most radars but that severely limits the range.
You can see why experts and others are confused, I am sure.
The ocean on the "other side" of Malaysia is very deep and if it went down there, it might be a while before it is found.
It is difficult for me to conjure up any rational situation of mechanical problems that would cause what has apparently transpired so far. It almost has to be terrorists of some description and they have at least one knowledgeable member.
Best regards,
RA1