I cannot believe that so many people have bet on the complete left field, long shot, outsider, as the cause of this accident. How many times has weather brought a plane down from the cruise? I would suggest that 1000's of aircraft have encountered CB's at altitude over the years, for one reason or another and survived.
What is more likely, something that has not happened before, or some form of mechanical failure, either latent, or caused by something either not doing what is should do, catching fire or blowing up on board the aircraft. That has happened many times and brought aircraft down.