On a quick note, future variations could make use of both sides of the connector, and the pins could become decoupled. It would require more complex circuitry in the plug and a updated connector on the phones, but that would allow a singular design today to be updated in the future with 2x the pins.
For people interested in the more technical implications behind this move:
People fail to grasp the reason USB 3.0 has so many pins. Its because the signals between the analog USB 2 serial interface and the SerDes interface aren't compatible, you'd blow out the SerDes drivers if you plugged in something that used USB 2.0... hence they doubled the pins and ran the signals side-by-side.
Interestingly enough, the USB interface with the iPhone no longer needs to fully reside on the phone. A chip could determine in the cable what you are plugged into at the host side and act as the physical interface layer, eliminating the need for the USB 2 pins going to the phone. Since we already know the phone supports HDMI over the connector, we already know the pins use a multi-gigabit SerDes.
What standards use multi-gigabit serdes interfaces (which are very standard)?
PCIe
USB 3.0
Ethernet (MAC to PHY)
SATA
HDMI
DisplayPort
and.....
ThunderBolt... as Thunderbolt is an multiplexed version of PCIe and DisplayPort.
Why does Apple call it a Lightening connector?
Maybe it supports a single lane of Thunderbolt in future hardware (or even current hardware). The DP/TB connector is dual-lane... a single lane would still provide a HUGE increase in throughput; you would likely never need more than that for interfacing a mobile device.
This connector, along with the ability to put physical layer chips in the connector, opens up the world to doing almost anything with the phone.
The real question I have is what is the SerDes hardware like on the phone side? I'm assuming most of these interfaces aren't supported due to lack of physical hardware. Without an FPGA or physical hardware, things like SATA, USB3, Ethernet, etc wouldn't be practical from software implementation... but the possibility for more and more protocols with future phones/devices is intriguing.