If a composite structure gets hit by lightning, the charge will tend to make its way through the carbon fibre and spark towards the nearest metal structure WITHIN that part of the body. This is fact. Boeing apparently know of this issue, airbus apparently know of this issue.
The horizontal tail fin of an A330 is made of carbon fibre. The tail section also contains a huge fuel tank!
Boeing, knowing about this problem have added a "Nitrogen interter" system to the fuel tank. This removes any air from the top of the tank, replaces it with nitrogen and in theory reduces the risk of a fuel tank explosion.
Airbus A330/A340 planes do not feature this system but instead rely on metal strips on the tail to conduct the charge away. The fuel tank has air in the section above the fuel.
Carbon fibre does NOT act as a Faraday cage. It doesn't conduct electricity.
Obviously, if the plane in question were hit by lightning on the tail section, the rear fuel tank *might* have exploded. This would be consistent with current reports showing TWO distinct areas of debris, ie the plane came down in two parts.
This would also explain why the ACARS system was reporting massive power failures but continued to function for a few minutes. It'd also explain why the crew failed to communicate with ATC.
This is obviously only a theory but it *could* explain the events of Sunday/Monday.