Dave, some interesting papers there - a lot to go through...
I'm still not convinced the complexity of variable diam is justified when variable rpm is also considered. Those centrifugal forces are not to be easilly dismissed. Even then most of these configs still struggle to achieve a low disk loading. And the mass of all those complicated mechanisms nibbles into payload. And as for modes of failsafe...
I'm still rootin' for X2, since to me it is the best way to get a helicopter to perform at speed.