Just suppose, wild speculation ensues...

Referring to AFLM's map image, IF (really big if) the person at the controls had an ICAO flight plan on file from say Perth to Kabul as a ferinstance, and it was activated when Flt 370 went dark, the "person at the controls" may have received clearance and a new transponder code, and then continued the flight under that new flight plan. By the time the peeps in Malaysia figured out what was happening with Flt 370, the B-777 could have been on the ground at some remote field.

I wonder if the folks in charge of this investigation have checked out every aircraft associated with a flight plan passing through that part of the world to ensure it originated and landed as reported.

Lots of speculation goes quite well with a good mystery. I have this gut feeling that tells me we haven't seen the last of that aircraft.