Wikipedia Dock Connector says:
"Many Portable media players feature a dock connector, such as the Apple dock connector, which is a proprietary 30-pin connector that is common on most models of iPods, and all models of the iPhone and iPad.[1] Originally, the Apple dock connector carried USB, FireWire, some controls and line-level audio outputs. As the iPod evolved, so did the signals in the dock connector. Video was added to the connector. FireWire was phased out of the iPods, which led to a discontinuity in usage of the dock connector. Older implementations of the dock connector may have been using the FireWire power pin to supply power, and cannot charge later iPods, iPhones, or the iPad, requiring an after market adapter to allow charging."
Since Thunderbolt talks in the listed protocols, Firewire, USB 1,2,3, Audio, all they need to add is power. It also widens the available protocols to various video formats and anything PCI. This is not merely a smaller hole in your iDevice, it is a broader compatibility with outside devices and protocols.
Expect to see some sort of converter for older 30 pin devices so newer devices can use them as currently expected for I/O and charging.
But new ecosystem devices will have far broader capabilities.
I just wonder if an iDevice is necessarily the end of a TB chain or if there will be a dongle/procedure to make it a pass-thru device as an option?
Rocketman