If your goal was to train hundreds of Jihadis in the art of hijacking modern jet-liners, then there is no real substitute for having the real thing in your possession - even if it is forever grounded in an underground bunker. You cannot just go and buy a 777-200 without leaving a trail. Plus a fair deposit......
I still wonder if the plane was stolen. No 'terrorist announcement' motive needed.
The fact that nothing has been identified is too mysterious. No oxygen masks, foam, rubber, sandals-nothing, 300 tonnes makes a big debris field, which expands exponentially over the weeks and months. All it takes is a single identifiable object found by a fisherman, beachcomber, surfer, coast guard, shipping or dog, in what is now a 12 month period.
Maybe it didn't 'go down' at all.