I got a 55" B7 today from Richer Sounds. I've tried the 4k HLG demo on BBC and found some 4k HDR footage on Youtube and my word does it all look stunning. It blows my previous Samsung JS9000 out of the water. I'd like to get a UHD blu-ray player at some point but at the moment I think 4k blu-rays are unreasonably expensive. I normally only watch films once or twice, so £24.99 seems pretty steep. That's over half the price of a PS4 game and those have more replay and sell-on value. For now 4k streaming through Netflix and Amazon Prime will do.
Speaking of prime, and as others have said, their 4k content is very randomly organised and difficult to find. I was trying to find a 4k version of the Grand Tour to play but it just kept on coming up with the regular 1080p version.
Found the same in terms of 4k blurays. I have an X1X anyway so the player front is sorted unless I feel an upgrade to a proper one but still stings paying that for some films. I went down the Apple TV 4k route for that for 4k films. A lot of the new films (seems to be most things except disney films) are in 4k dolby vision and dolby atmos is soon to come in the new tvOS release in september. Helps that the maximum a new film is, is about £14, with many older being down to £4-8 and full whack for a 4k bluray for disney releases lol.
Prime is just a bit of a mess for content discovery. You got to keep scrolling down for ultra hd content, or maybe searching ultrahd or ultra hd may work.