It does exist-- from hobbyist entrepreneurs. 51nb has been selling motherboard upgrades for the old 4:3 ThinkPad models for a few years now, and others have begun to specialize in whole-system integration, additional mods, and complete systems based on this work (I'm one of those people, though I also do it as a hobby).

My three ThinkPads X60s machines are all Broadwells, with nice 12.1" 4:3 high res screens using modern backlights I fabricate myself. They work so well I intend to build more.

Well, there is the problem. If monitors and notebooks are sold with 16:9 only, then of course there is no "demand" for 4:3, because you don't sell any! This argumentation is scewed.

You assume there is actual competition taking place in computer display panels. Not sure how you can get that impression.

There's a demand for a non-anemic Mac desktop that isn't a huge overpriced dead-end waste of money, but that doesn't exist.

Just like title loans, reality tv, and vape shops.