From the latest AAIB update, it is clear that the problem was either fuel starvation or fuel aeration. As far as I can see, there has been plenty of speculation about fuel stavation/ icing but little about fuel aeration ( I have not followed the whole thread)
So, where can significant amounts of air get into the fuel? Apart from the tank vents and surge tank ( which aerate the tank system normally and are above the tank fuel level, anyway) the only other way in which the fuel system can be open to the air is via the fuel jettison nozzle valves. If these were to somehow be signalled to open, there would be a large diameter pipe, open to air, which is routed via the override/jettison pumps into the same area as the wing tank pumps. It might then be possible that the wing tank pumps would ingest both air and fuel, leading to fuel starvation in both engines.
The time difference in the power down of each engine could be explainable by differing amounts of residual fuel in the jettison line to each wingtip.
This speculation could explain the simultaneous failure in two 'independant' systems. However the question would have to be: what could signal the jettison nozzle valves to open independently of the jettison master switch. Maybe EMI or a software glitch? Also, I have no idea if the override/jettison pumps are an axial type without any kind of reverse flow check valve, which would allow air to pass through.