I still think you're making a false equivalency between pixels and sub-pixels. If you look at a microscopic view of an LCD, it is not a seamless field of sub-pi

I still think you're making a false equivalency between pixels and sub-pixels. If you look at a microscopic view of an LCD, it is not a seamless field of sub-pixels--substantial surface area is non-emitting black borders between them, but the eye merges the sub-pixels (and pixels, if sufficiently high density) into a unified light source. Adding white emitters does not inherently mean you are getting "less color" -- many factors influence the blending that you perceive. It does, presumably, mean that colors at the highest brightness levels are less saturated, but that may mean you are getting additional, less-accurate color space, without sacrificing the accuracy of the color space you already had. I have no idea if RGBW displays on the market actually have these characteristics, but your dismissal is based on a misunderstanding of the optical properties at play.