It is clear that there was a logical disconnect between the Stall and Autotrim. Had there been a logical connection, with a locking of the THS in Neutral, it would have certainly helped the pilots, the recovery from Stall.
I think you have to be careful what you ask for.
- Making the trim operation audible (this seems like a no brainer). Relying on the visual cues seems over optimistic, particularly when things have already gone pear-shaped.
- Auto-neutralizing trim state in stall warning. Unless I am misunderstanding things here, the trim was not what stood this aircraft on it's tail, it was the PF elevator input. My understanding is that the elevators alone can override the THS. Would neutralizing the THS have been the key here to save the aircraft? I don't think so at all. The PF (and PNF+Captain) at no point acknowledged the STALL. In fact the PF was demanding NU pitch for most of the time - he got what he asked for. Would the PF have NOT demanded NU if the THS has not followed his demands... or had untrimmed? Doubtful.
I do believe a better more explicit YOU ARE STALLED alerting system can be implemented. The aircraft knows enough from AoA, Vertical Speed and perhaps Ground Speed to be able to state quite happily "You are stalled and plummeting to certain doom - how about reducing AoA with a bit of nose down old chap...". OK may be that's a bit glib, but something beyond the existing Stall Warning audible ---> "AIRCRAFT STALLED! AIRCRAFT STALLED! REDUCE AoA!"