Masterpiece: Sigh... I hate the 4k label, it's 2160p
I believe some caution needs to be exercised with purchases currently, there will be some compatibility issues with displays and peripherals until the delivery system standardizes.
Just consider that from HDMI1.0 which took a number of years to settle too 1.4, HDMI2.0 became 2.0a recently to include HDR, but really there is no content yet, not unto the players actually come to market, which may be 2~3rd quarter this year. There will be revisions once these come to market, that is the harsh reality, but I see obsolescence with displays right now.
Another issue with HDMI, I'm just testing a video processor which is a 4k in and output device. It is becoming apparent cables are going to be a problem for some. The new HDMI 2.0a 4k chips are sensitive to cables, where active cables seem to work best. There are cheap active cables, so it isn't so much a cost thing but a type thing. Can your wall run HDMI cable handle 18Gbps?? Many are just 9Gbps. I'm have trouble with a RX-A3040 receiver in this mix as well.
With the above, be aware that currently Rec2020 is not being implemented yet other than resolution which is for the most of us an up scaled video processor(if you have one) or display result. Currently you only have Rec709 at 8bit with more resolution.
When the players come, with a 2160p source it could well be 10bit at true 422 or even 444
Personally I'm not going 2160p until the transport and some content is on the shelves.
Oh the size and distance thing, I sit 3m from a 106in screen and it's verging on being to far(about 30degrees viewing angle). For 2160p I'll probably go scope 2.35~2.4 out to 120in+, and stay at 3m distance.
The problem with displays even 75~80in types, is that to appreciate the 2160p material you need to be about 2m from the screen. From memory roughly 50degrees viewing angle. Frankly I find panels uncomfortable at close ranges.
However as others allude to that they find the viewing distance thing difficult, part of this is explained in processing, steps and increments in grey scale with correctly adjusted white balance and ETOF(gamma in old terms) convince your brain of greater sharpness, detail and even more apparent colour.
Just some things to consider at the moment.