The pictures of the tailcone show a long section of pipework known to be (from schematics and factory photos previously posted) the APU fuel supply pipe.
_If_ the cone detached either as the initiating event or as a result of VS/HS fail, would not the yanking out of this pipe cause a fuel leak capable of causing an explosion? The length of the pipe shown probably isn't sufficient to reach the centre tank, but by my non-expert reckoning it would be forward of the RPB.
I'd have thought if the APU isn't running their would be an isolator on the fuel line hopefully at the tank, but what if that failed or was left open (yes I know, Mr Occam is getting less happy as I go on, but still...).
Lastly, is it at all possible that the APU was actually running during the flight? I imagine there would be plenty of cockpit indication of that but it would enable the fuel leak - or possibly even APU malfunction of some kind. From photos I'm not suggesting destructive failure of APU, but possibly vibration, along with corroded cone attachment due to skydrol leak assisting cone departure or somesuch ...
The HS detachment seems to have taken most of the fuselage below it when it went. Surely the long pipe section implies that the APU tail cone detachment preceded HS detachment, and if so rules out HS detachment as cause of the curious clean detachment of APU taile cone?