> it's not (yet) practical to cram them all into an on-screen pixel At the pixel density (>500,000 subpixels per square inch) of current flagship smartphones,

> it's not (yet) practical to cram them all into an on-screen pixel At the pixel density (>500,000 subpixels per square inch) of current flagship smartphones, I think it would actually work just fine to have 6 or 9 (or whatever) different primaries, make a grid of little pixels in some scattered but regular arrangement, and then use clever digital signal processing to figure out how to convert an RGB image into a RR'GG'BB' (or whatever) image. I would expect it to look visually identical at typical viewing distances for existing images, while potentially allowing someone with low-level hardware access to make a wider gamut / choose their preferred metamer / etc. I would expect it to be entirely achievable using current technology and not inordinately much more expensive than current displays. But the engineering effort and additional complexity might not provide enough benefit for display vendors to invest in that, vs. just continuing to optimize their current display concepts. Or they might not even be considering radical changes in strategy.