So here's a thought I had - it's 3:30 so forgive me if it's stupid.
Anyway, what about using a microcontroller that has a built-in USB interface? What got me thinking about this is the atmel AT91SAM7S series has built in USB, as well as a bootloader that can download new firmware over the USB connection.
Clearly this chip is pretty serious overkill for our needs, but there are stacks of similar, but simpler chips that'll save a bunch of effort for anyone who doesn't want to buy/build a programmer as well as a bunch of triggers.
The bootloader will also make the whole multiple-personality trigger thing a whole lot easier to deal with, if that's the route we end up going.
Anyway, atmel has a bunch of USB-capable micros over here. There are a bunch of PIC's, and some more from silicon labs.
Anyway, I'm sure you get the picture now...there are tons of cheap micro's out there that support USB natively. We can add that functionality for basically the cost of the connector.