Nice share mate!
It was fun how the guys got puzzle with a palette image and a 186 processor inside the monitor ...
I haven't checked the specs of the display they used... but, at first glance spying on somebody's screen doesn't seem feasible without a hardware modification. The link to the DEFCon presentation is in their github
The only output channel for the processor in the monitor seems to be the uplink USB as far as I understood. It is unlikely they use USB3, so you just do not have enough bandwidth to transfer the image and a 186 does not looks powerful enough to compress even one low res frames every X secs... According to wiki, 80186 had a blazing clock of 25MHz max... Even if it carries an special version of the processor clock will probably be in the MHz range.
In theory it may be possible to do DMA transfer directly over USB (there is probably not enough internal memory to buffer the data), but that will require special SW in the computer used the monitor. I do not fully know how does that DMA over USB work but I think it will have an important impact on the overall performance of the system.
It is a very interesting topic. I loved it. But IMHO, the sites publishing the news were a bit sensationalist.
@Cromical all the Tempest thingy is also pretty interesting but it only makes sense on CRT displays... thousands of Volts in a Tube firing electron rays against a phosphor screen with high magnetic fields to deflect the ray.... a different technology.