Spoilers:
The trick was pretty easy to guess but still a lot of fun to see put into practice. The EGA monitor bits, and more broadly just the idea of trading color bit depth to multiplex signals for multiple monitors into a single framebuffer and physical output is pretty cool. The Windows display driver idea actually implemented on real hardware would be tons of fun. I could have seen products actually doing this "back in the day" to do multi-head setups. I'm kinda surprised examples don't exist.
I think it's just that monitors were so much more expensive then, especially those capable of the 350-line EGA mode.
"Every mathematician wants to discover a mathematician's lemma."
It might have been easy to guess, but you didn't really think of it in the past 51 years since the Commodore 128 was introduced, did you?
Since everyone is vibe coding everything anyway I fully expect there to be a Windows 3.x display driver that works this way soon. I'm sure people in the retro computing hobby feel a certain way about this, but it's definitely also hard to deny the amount of "Project Structure" in README and "// ---- Input Handling ---------------------------------------------" snippets I've been seeing lately in a lot of new homebrew and other projects. (Another fun one: comments that are justified to a specific column but off by one in only one of them. I'm sure humans do this too, but AI does it more.) I don't really care that much personally although it's silly that people kind of have to be wink-wink-nudge-nudge about it for the foreseeable future.