Fire hypothesis
Swissair 111 offers the best comparison for a hypothesis. The electrical short caused a fire, which was detected by the crew 53 minutes after departure. 13 minutes after that a rapid succession of aircraft systems failure were recorded on the FDR`s. About a minute later comms and SSR were lost. About five minutes later the aircraft crashed into the sea. The crew must have become incapacitated in that time frame of 14 minutes. In the case of Swissair 111 the fire was all too consuming so as to incapacitate not only the crew but also the aircraft.
In such a scenario, in the case of MH370, it follows that the crew alone must have been incapacitated, the aircraft`s flight control systems must have proven sufficently robust and in conformity with their manufacturing specifications and design criteria for the aircraft to have remained aloft for such a long time thereafter. In such a scenario a ground alert system for crew incapacitation, and for its associated remote and/or on board auto electronic reversionary activation and control system ( analogous to drivers safety device "DSD", also known as a dead mans handle on trains and kill switch on boats) could provide a further redundancy measure for future flight safety. In the case of Swissair 111 the recommendations had also referred to a cockpit camera, installed as part of a such a system, along with continuous flight monitoring, would also be a further deterrent to unlawful intereference with an aircraft by any persons on board.