Have we ruled out the Max's FBW spoilers?! On the NG and previous the spoilers/ speed brake were cable/ hydraulic. On the MAX they are fly by wire. The change from cable/ hydraulic to fly by wire is a *HUGE* change in the flight control regime. The Max spoilers have various complicated automatic triggers that could have a complex interaction with other systems. On the NG and previous the symmetrical spoiler deployment could be overridden by stowing the speed brake handle. The automatic deployment is very difficult to override on the Max. One has to reach up and move a guarded switch. That motion is not a memory item nor is it intuitive. On the NG and previous, symmetrical deployment of the speed brakes / spoilers was indicated by motion of the speed brake handle. On the Max the spoilers deploy for various MCAS and non-normal scenarios without proportional movement of the speed brake handle. That means the pilots (1) are not aware of their deployment, and (2) cannot easily override their deployment. IMHO the precipitous and unrecoverable descent would be consistent with un-commanded spoiler deployment. The FDR will confirm or refute my opinion, but regardless, changing a major flight control from manual - cable/ hydraulic to fly by wire is very suspect. I don't know if there is any precedent for a derivative aircraft being introduced with a major flight control system being changed from manual control to fly by wire without a new type or at least difference training being required. The differences training between NG and Max was about 4 hours of CBT... I have NG pilot friends who were signed off to fly the MAX without so much as a sim session.