You may be underestimating the desire to earn through differentiation.
Assuming the product companies accept the plateau on resolution (I agree it’s likely), there are many ways to exploit the other stuff. Colour space, tacling each type of compression artifact, additional channels (probly not long until we have HDR RGBW), etc etc and those will each come with their committees made of patent-hungry companies seeing non-encumbered encodings as “undesirable”
I don’t think it matters in a practical sense. Our streaming overlords have already shown that by crippling the effective color space of supposedly 4K video they care little for quality of broadcast. Crushed blacks and smeared video are all you’ll get no matter what the standards say. They were, are and remain terrible on 1080 video, 4K is a farce.
You’ve missed the point: each addition can (and likely will, based on history) be the way to bring more patents into the market. It rarely has anything to do with objective quality (except in the marketing)
You can only ask so much more before customers stop buying your "better" product without seeing some real value. 4K HDR is already at that point (for home video releases anyway).