The actual crash might be more about hot weather high mountain flying and maneuvering.
But the post-crash in-depth wreckage analysis is said to have revealed unexpected fatigue and non-standard repairs to word it polite. This will be the part the Dutch will have a look at.
Spot on, LessHair. The delay in publishing the final report is not because of any doubt to the primary cause. Its because the whole outfit was operated in a rather amateurish way which did not really match the stringent commercial rules that apply when you sell flight-tickets to the public. The BAZL (FOCA or Federal Office Of Civil Aviation) had a blind eye on this outfit because it was mostly run by well-known and well-liked military aviation oldtimers. It will be difficult and critical to word the final report, as it will most likely trigger legal battlements (insurance) and possibly criminal investigations. And if indeed the oversight of the FOCA was producing holes in the Swiss Cheese, state liabilities might matter too. Sad for all those involved.