For those who've looked through the Kindle source code, is there any possibility that the ability to connect an external keyboard (like the ones you can use with windows mobile or the iPhone) can be added to the kindle (either via a hack or officially) on a future date?

For a student using the DX to annotate for example, the buttons on the keyboard are I think very stiff and don't really support note taking.

Highly unlikely.

Right now the Kindle is only configured to act as a slave device, so you can't just plug a USB accessory into it. Theoretically, the chip supports the ability to act as a master device, but it would require programming in code far beyond what's available to support on the Kindle.

Assuming you had a root shell on the kindle, it'd be pretty straightforward. You'd want to build the kernel sources that amazon provides using /proc/config.gz from the Kindle. After that, a couple insmods and you _should_ be all set.

That said, it'd likely be sort of painful, especially since nobody has a console talking to the kindle framebuffer yet.

At least one USB host is used for the CDMA card inside. Like all other WWAN cards It's connected via USB. I could even put it in my laptop.(I have no drivers as of now, and I don't live in the US.)
So You could make a passive mechanical adapter to get a normal USB port, put it in a USB Hub and have plenty of USB ports to connect everything you want.
Details at the end of this page:
http://ikindle3gs.eu/
Some adapter that -might- work:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=270424109733