This HDR obsession makes me want to abandon color entirely and switch to E-Ink.
It's even faster if you let it manage its own pixels and only update parts of the screen that need to be redrawn. Can't play videos like that but scrolling a spreadsheet becomes much faster.
Have you actually tried? Do you have a video of this? Because as far as I know, and I actually work with electrophoretics, physics limits the speed of the ink. I hope you're not confusing something like A2 mode with actual display updates.
I don't understand what you mean by "poor gamut". Gamut of grayscale?