Thank you (in chron. order) HarryMann, gums, PJ2 and John T. for providing some very usefull informations about longitudinal stability (or instability) related to CG position.
My question was also aimed at this aircraft pitch authority (or lack of it) once stalled at such an AOA : If, after a while, a recovery was attempted, the issue faced by the PF could be that he could lack the necessary pitch down authority in order to regain some lift.
If I understand correctly, assuming that the elevators were not fully stalled, an aircraft with an aft CG would have to be pitched down to a lower angle-of-attack but would also have a better pitch rate than with a more forward CG. On the other hand, more forward CG doesn't help for stall recovery but it's better for avoiding to enter the stall at the first place.
Then AF447 had a less than optimum lift cruise CG that did not prevent it from stalling without being (in theory) as much helpful for a recovery attempt.