Afew thoughts on the speculation:-
Contaminated fuel - there was in incident of fuel contamination out of Lagos during the 90's. 4 aircraft were affected, 3 northbound and 1 southbound. The indications were of fuel filter blockage and not all the engines suffered at the same time, so I think it is an unlikely situation for the BA 038.
Fuel icing -as the fuel would be configured tank-to-engine, unlikely that both engines would suffer loss of thrust at the same time and surely the engines would 'cough and splutter' or surge?
Fuel starvation by configuring both engines to one tank -the AAIB has not indicated in it's interim report that a lack of fuel was found in either main tank, so again, and given BA's SOP'S, unlikely.
Pilot error in shutting off both fuel control levers during the approach - very, very unlikely.
Software glitch -perhaps due to condensation? Maybe not just due to condensation, but perhaps that one-in-a-billion statistic?
My money is on an electronic fault between throttle and engine.
Airframe by Boeing
Engines by Rolls-Royce
Micro-chips by Sum Ting Wong Electronics Ltd.