It may take a while (years because that's the speed of governments) but I would say that it is very likely that all airliners (passenger and cargo) will eventually be required to have tamper proof transponders...something that can only be accessed by lifting the hood when the plane is on the ground and stopped. I can think of no reason why a pilot or anyone else in the cabin should ever need to disable one.
Different issue: The plane is supposed to be able to fly 7+ hours with a full load of fuel depending on altitude, speed, head or tail winds, number of ascents and descents, etc. However, it is my understanding after reading a few pages of
this forum that planes are usually fueled for the anticipated trip plus a little more in case of trouble. In other words, they almost never top off the tank. But...this being Malaysia, there are no records and no one knows how much fuel the plane had. So...I'm not sure that any conclusions can be made regarding how far the plane could have flown. As regards Somalia, someone on the pilot forum said that Somalia would be on the very extreme edge of the plane's operating range if fully fueled so that kind of seems unlikely. Unless refueling is involved. And if it is then there would be other possibilities for destinations that would have to be considered.
Yet another issue: Assume a hijack. There are only three possibilities. 1) The crew...one or both pilots...is responsible, 2) A passenger or...more likely...several passengers are responsible or 3) Both crew and passengers are responsible. Any other possibilities require science fiction or magic. I don't know what investigators have found regarding crew and passengers. I know
of some things, sort of, if you can believe everything printed by the media...such as regards the Iranians with fake passports or that the pilot had a homemade flight simulator at his house and that his wife and kids left the day before the flight. I say that
I think I know these things because they come from the media and the media is frequently a source of incorrect information. But...what I said about the hijack possibilities is based on reasoning rather than data and I don't see any problems with it. So, that said, sooner or later the investigators will turn up some clues about the crew and/or passengers that may reveal a means and a motive for what happened. It could be a very long time depending on who the investigators are but mysteries want to be solved so it should be forthcoming at some point.
One more point regarding hijacking: Motive possibilities. 1) Hostage taking for ransom, 2) Hostage taking for terrorism, 3) Plane stealing for terrorism (i.e. weapon delivery system), 4) Pilot or copilot suicide, 5) Political statement by unknown persons for unknown reasons, 6) Something else because...crazy. There could also be something else that isn't crazy but crazy has to be on the table. I'm not including suicide as part of "crazy" because it is a whole different subset of "crazy." Crazy can include all sorts of irrational reasons that don't occur to us because we are not insane. But I can't think of any other reasons to hijack a plane.
If a debris field at sea doesn't emerge within the next week or so then the thing had to go down on land. Somewhere. And short of the thing being completely disassembled and buried it should be found. Wreckage or intact, if it isn't on the bottom of the ocean it will eventually turn up.