Commercial shutdown controller
I guess I'm a little surprised at the lack of options for a commercially manufactured/available shutdown controller.
I remember even as far back as Win NT and Win98 (perhaps even Win95), we would hook our servers up to a UPS via a serial cable. If the UPS sensed a powerloss, it would, of course, keep you going for a couple of minutes... but then it would send a signal via the serial cable to the PC and Windows would automatically shutdown. This was a built-in feature of Windows. Indeed, I just checked my Win2K machine and my XP machine and they still have the same UPS configuration dialog that allows you to set this up.
So it doesn't seem like that far a stretch for a DC-DC (especially one that connects via cigarette lighter... ie - made for automobile use) to incorporate this same functionality directly in the converter. Provide a serial out that behaves like a UPS and sends a signal to shutdown Windows.
I've searched and searched in these forums and have only seen a mere mention of this functionality. I've goggled for a couple of hours and haven't found much more.