The worst part of Blu Ray is color subsampling and sticking to REC709 color standard without alternatives. 1080p YUV 4:4:4 cinema color gamut would look a lot better at 40 Mbit/s h264 than what we can have now. No Red Ray needed for better Blu Ray image quality. But an even more efficient codec as Red Ray apparently is that can do 4K from Blu Ray is very welcome, of course. If you did 4K with h264 at 40 Mbit/s it would also look better than what we get now from Blu Ray, simply because going from a lower resolution to a higher resolution source helps improve apparent image quality, even if you stay at the same bit rate or do not go up a lot. 9 Mbit/s 720p/1080p looks usually a lot better than 9 Mbit/s SD (as from DVD) and
20 mbit/s 1080p better than 250 Mbit/s SD studio masters (there is no comparison). You can not make up for missing detail and sharpness by reproducing random noise very precisely. This effect alone makes 4K look better than 1080p at comparable bit rates. The artifacts at 4K pixel size tend to become invisible while the additional detail and sharpness is quite visible.