In this hypothetical situation the question is -what caused the main wing to stall in the first place ?
1 Why the lack of speed ?
2 Was there an engine problem or maybe an inaccurate airspeed indication?
3 Was ice creating extra drag and if so how come the FDR shows
the autopilot did not trim to compensate?
4 Surely the above scenario looks more likely than a tail plane stall
as according to the NASA icing video a severe pitch down would have
occured first in that scenario?
And the obvious question number 5, why didn't the stick pusher prevent the stall from occurring?