Is the Lightning connector 8-pins or 8+1 ground pins?
If you count the shield on USB 3.0, the "9 pin" version actually requires 10 pins, as the shield, while typically grounded, is not actually used as the signal-ground (and it cannot be used as such).

As such, if the lightning connector indeed has only 8 pins, there is no way it can support USB 3.0 while properly complying with the USB spec.

I would guess that if it supports USB 3.0, it would be with non-standard USB extension, much as many of apple's other USB addons (like their high-current charging facilities).

I'd like to further note that, from an electrical engineering standpoint, using the casing (which is called the shield) for anything but, well, shielding is considered very bad practice.  

The entire point of shielding is to basically absorb any interference before it can each the inner conductors. If you are relying on the shield for carrying a meaningful signal (and ground is indeed a meaningful signal), it is no longer effective as a shield.



If it does support USB 3.0, I would hope they open the connector mechanical design up for wider adoption, as the current USB 3.0 micro connector is horribly designed mechanically.