Taking a deep breath, I ask if we can possibly summarise what is known or can be REASONABLY deduced out of all this dross? I do, however, feel that we can rule NOTHING out at this stage:-
1) Is it safe to assume that the apparent sequential system 'failures' were triggered by the weather conditions in the area?
2) Is it safe to assume that standby attitude would probably still be available? (difficult to determine above!)
3) Is it safe to assume that engine control would be unlikely to be compromised by the known 'failures'?
4) Is the reported 'inability' of the AB 330 probe system to cope with 'heavy' icing a fact, or just more of the rubbish here? If known, was there any qualification to the release to service (icing) and if not, why not?
5) Has anyone yet established what MEL items were extant?
I'm not sure how many pilots here have actually experienced 'severe' turbulence in an airliner. I have, once, and I was scared (and I do not scare easily). If we interpret the 'hard' turbulence report as meaning severe, I pity that crew. Throw in system 'failures' and it is a one-way street in my opinion. In my experience, we had to make an emergency descent to avoid loss of control (737 with ALL systems working), and I can assure all that it can be extremely difficult even to think rationally in that situation. I was waiting for 'something to break', and needed the Boeing 'yoke' to hang on to, and I do wonder how you cope with a tiny sidestick? Can you avoid involuntary inputs while being tossed around?
Moving on, NB away from facts:
I would expect (my supposition only) that the crew were left with no option but to make a descending turn-back. That there was apparently no call (heard) to advise other traffic (iaw oceanic procedures) I find surprising as it is a fairly high priority matter, more-so than position reports. Assuming they were operating IAW SOPs therefore I suspect they were already out of control at this point.