What I would like to see in the PS5 and PS4.5 (being a UHD blu ray player)

[SvennoJ]

Uhm, chroma 4:4:4 sampling is essentially the same as RGB in data transfer terms, just different color space on blu-ray. 10 and 12 bit color are already supported on XBox one perhaps ps4 too. I guess it is, it's called HDMI deep color (was already supported on ps3) Sony's 4K mastered blu-rays use XvYCC color space, 1.8x bigger than the standard rec.709, yet still limited by 8 bits encoding. (It's a clever extension on rec.709 that some tvs support)

But true, you need HDMI 2.0 for 10-12 bit 4K at 60fps. HDMI 1.4 tops out at 24fps 8 bit 4K.
However 4K UHD blu-ray movies still use 4:2:0 chroma subsampling and are limited to 10 bit. Still a big step up from blu-ray thanks to 10 bit color Rec.2020 yet not what you get in the cinema.

When you buy a 4K tv, make sure it has a 10 bit panel, otherwise the biggest advantage of 4K blu-ray is lost.

In theory a 4K 4:2:0 blu-ray should be able to be downscaled to 1080p 4:4:4 deep color, but I don't know if anything will do that.
(4K blu-ray has 3840x2160 gray scale, 1920x1080 color info compared to 1920x1080 gray scale, 960x540 color info on regular blu-ray)