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.
If you keep reading...
Connectivity
In contrast to Steve Jobs' announcement at WWDC 2010, recent Federal
Communications Commission documentation has shown that the iPhone 4
contains a penta-band 3G UMTS antenna, not a quad-band 3G UMTS radio,
as advertised by Apple.
According to the FCC documentation filed by
Apple, the radio inside the iPhone 4 supports 800, 850, 900, 1,900,
and 2,100 MHz. The 800 MHz frequency, which is most commonly used in
Japanese mobile phones, is not advertised as being supported by
Apple.[51] However, the 800 MHz band is a subset of the 850 MHz band,
which probably explains why the device is advertised as
quad-band.[citation needed] The chip-sets were manufactured by
Skyworks Solutions[52] and Infineon for GSM version.
Best Answer
If you see a M3, M4, T3 or T4 on the box then the phone has been designated as HAC compliant.
About the T
source: betterhearing.org
About the difference between M and T
source: uscellular.com