Question - some of the rotor aircraft shown had a sort of ring structure enclosing their rotor blades. Anyone know whether that is purely a safety mechanism (to prevent the rotors from contacting structures and/or faces), or whether there is some aerodynamic benefit?

There's a very perceptible aerodynamic benefit on large aircraft, assuming the extra weight is negligible to the project's scope.

The ring kindda cancels out energy loss due to air escaping the blades sideways, instead of only downwards, so you have a better 'use' of the air the blades move. It's obviously far more complicated than that, but basically, that's it.

Question - some of the rotor aircraft shown had a sort of ring structure enclosing their rotor blades. Anyone know whether that is purely a safety mechanism (to prevent the rotors from contacting structures and/or faces), or whether there is some aerodynamic benefit?

I thought the medivac bed thing was pretty neat. It was hard to tell what mechanism they were envisioning bringing it up to the main aircraft - maybe it's electromagnets or something?

Some of the concepts were a little more Halo-esq, but there were also a few that reminded me of Destiny. Such as the tilt-rotor-VTOL, and how it converted to a jet (reminded me of the VTOL dropship in the Destiny gameplay), and also the little drone that popped up and gave the soldier a birds-eye view of his battlefield reminded me a little of the Ghost - just less glowy. :)