Fair enough, but you should never ever do this for images intended for display on emissive displays, unless the goal is narrowly to preview an image for print,

Fair enough, but you should never ever do this for images intended for display on emissive displays, unless the goal is narrowly to preview an image for print, and even for that it's probably not a great idea. For a general purpose, the results will just be bad, and anyone putting such images on the web is doing it wrong. Oklab / Oklch is a different topic than the display of bitmap images, so if CMYK JPEGs is what you had in mind it's a bit of a tangent.