Yep! I remember doing this on the HP 48G's in the mid-90's: https://www.hpcalc.org/hp48/graphics/grayscale/

The computational and engineering effort for these hacks to get to those results in production would have made those price sensitive consumer gadgets far more expensive. It just wasn't economically feasible.

Also, if I'm not mistaken, those hacks look good on static images but could produce nasty artifacts on moving images.

TI-83+ calculators were doing grayscale like this 20 years ago, so a lot of people did have this as kids. It was a bit flickery but worked well.

They actually gave an example that was, the Gameboy. I think in that case the big issue for going beyond just 4 gray levels is RAM and ROM space, and also potentially the speed of the PPU and display driver in dealing with the extra data.

We were! When I was a kid 28 years ago I had an HP48 calculator that people used the same techniques with for some games and such.

There's a ton of monochrome screens available to EEs under $20, even under $10.

This is still quite relevant.