"Eliminate all other factors, and the one which remains must be the truth." - Sherlock Holmes
The AAIB seems to have pretty much eliminated mechanical and/or electrical failures within the engine systems as likely causes of this accident. They are not even suggesting that the cavitation damage within the fuel pump ocurred immediately prior to the crash - it might have happened weeks before the accident. The evidence points to some fuel related factor as it seems to be the only thing common to both engines. Perhaps, there is some aspect of fuel behaviour, under certain conditions, which has not been encountered before and is not yet understood. Cue the fuel chemists!