New idea / new worry (dinner conversation with other computer security geeks can be dangerous):

PCIe is the protocol used by hardware devices to speak to the rest of the computer, and includes direct access to RAM (DMA). It's previously well known that the Firewire ports on most computers can do the same thing and can form the basis of an interesting physical-access attack to a computer. (It's also used for remote kernel debugging.)

Thing is, when your monitor port now allows the remote peripheral to DMA with your computer's main memory, you've got a new threat... the hostile monitor/projector threat. You're traveling. You connect your computer to the hotel's digital TV or to the conference's projector. What if that projector is evil? Now it gets to interrogate your computer's memory or talk to other peripherals like your disk.

There's just no end of risk here. The only saving grace, I think, is that Xilinx FPGAs aren't fast enough to keep up with the raw data rate on the port, which means you'd have to have an appropriate driver chip. I'm sure Patrick could probably ballpark the cost and components of a suitable daughter board to shove into the back of a TV that would be able to make DMA queries and save the results to a memory card. I'm guessing it's not that hard to do.

What I'm less sure of is what you might do, in your computer, to deal with such threats. Can you imagine your computer popping up some kind of dialog box? "Hey, there's a new device out there. Allow it to connect?" I'm sure those would be popular with users.