789 Flight Safety
As I see it ,if Autopilot kicks out because of stick push, and/or of running out of trim to hold the nose up there cannot be a further pitch up of some 30 degrees caused merely by nose up trim . Something else must have been added at the same time.
I feel that deep stall is unlikely because this is not a swept wing.
We need a precise time line of events.
Did flaps stop at 20 degrees or did they go from 25 back to 20, which might move Cof P forward a little?
I see it being plausibly suggested that an unrecognised stick push could have been mistaken for Tail ice stall with an instantaneous decision called for to pull or to push.(I was caught once with iced up ASIs , Altimeters and Vsi in a similar coffin corner situation, in the dark ,with buffet; we didnt know if it was compressibiliy or normal stall, fortunately we had height and time to discuss and find other clues)
But I also understand from a recent comment here that the aircraft may have after all been intercepting the ILS from the wrong side , with associated notamed problems