I think that the rupture of the crew O2 bottle in the E/E bay could cause the failures we have seen in MH370. Due to it's immediate effect I think it fits better than the fire scenario. An O2 bottle failure is not without precedent, happened on Qantas QF30 in 2008.
Possible sequence of events---- 1/ Rupture of pilots oxygen cylinder in e & e bay and puncturing hull. 2/ Pilots incapacitated due hypoxia. 3/ Transponder box damaged in e&e bay as in close proximity to bottle. 4/ Autopilot and autothrottle also disabled. 5/ As trimmed for cruise aircraft could roam the skies until fuel exhaustion. 6/ As no debris found in sea after all this time, then maybe it crashed into jungle near southern Sumatra/Java, close to the final arc.