lomapaseo,
Do any of the manufacturers altually demonstrate a shaft separation at takeoof conditions, or do they just point at some design feature that might have worked in the past?
What you do is understand this is a possibility, and you design so that if the power drive arm would fracture releasing the turbine wheel from the shaft, it would not reach an overspeed condition where the disc would come apart. Although this was done on previous Trent engines, it wasn't done on this engine. It wasn't a lesson learned, it was a lesson forgotten, simple as that. You don't have to demonstrate it, you just use experience and good common sense to prevent it.
TD