A more mundane and common use of this technique is for reading the displays of weighing scales, digital micrometers, and similar instruments which did not originally have the feature to enable computer connectivity.
In my teens, I built a digital serial interface for a scale company my uncle was a salesperson for, think highway and landfill truck scales. This is how I built it, very straightforward to your point, mitm from the scale to the display.
Analogue hole is how I did a more efficient smart garage door hack than what people were talking about here at the time. Soldered zigbee switch into the physical button; worked great :D
I had a similar idea to bypass DRM for a while. Some kind of board that goes between the display panel driver and whatever sends it the signal, and outputs something you can capture, e.g. DVI or unencrypted HDMI. Not sure how practical it is.
In the past (circa a few years ago) the connection between the main board for a display and the glass driver board would be a ribbon cable, LVDS signalling. Very straightforward and typically not soldered. There'd be a ribbon cable connector. So yeah, you could just put a board between easily. And there are LVDS to H264/H265 chips already.
But as the other comment points out, older HDCP is broken wide open so ... easier to just use that. Plenty HDCP strippers on the market.
