The QF requirement for all crew to be seated when the seat belt sign is on may well be due to the company's obligation to provide a safe working environment. ie. If the pax need to be seated, so should the cabin crew etc etc.
The QF pa's specifically say that all pax must (repeat must) keep the seat belt fastened when seated.
The unfortunate by product of the above is exactly the situation that many QF flight crews go through every day - possibility of turbulence, but nothing untoward as yet - do we or don't we turn on the seat belt sign?
It would be interesting to see where QF stands legally in a court action with this scenario - ie seat belt sign off, turbulence possibility - some pax / cabin crew out of their seats.
As far as the 330 goes, it would have to be an extreme upset for the control laws to translate into abnormal attitude protection. (The actual numbers are reported elsewhere)
If the vertical excursion was in the order of some hundreds of feet, then any loose object would be subject to significant displacement, particularly towards the rear of the aircraft.
If the autopilot remained engaged, and normal control law remained active, the associated flight control ('g' loading) inputs should provide the best protection.
If the autopilot was disconnected manually as an instinctive reaction to the initial onset, then the crew has the capability to generate significant elevator input (with obvious results at the rear of the cabin) during the recovery process.
This will be an interesting investigation.