I assume the 4:2:0 limitation at 4k 60Hz is a bandwidth limitation for HDMI.
Although I assume that 4:2:0 at 2160p should be better than 4:4:4 at 1080p?
I've been trying to find a copy of the HDMI 2.0 spec but I don't think there is anything available on the web yet.
As I understand it, 4:2:0 is optional with HDMI 2.0 - I certainly hope it is, because things like 32 channels of audio up to 1536kHz seem like a complete waste of bandwidth.
The reason that 4:2:0 is being added, is because it saves bandwidth, and it lets you use cheap players as source devices. Prior to HDMI 2.0, the minimum chroma resolution you could transmit was 4:2:2, which means that playback devices are required to do a minimum of 4:2:0 > 4:2:2 upsampling.
Part of the reason that madVR's chroma upscaling is so good, is because it has access to the unaltered 4:2:0 data. With HDMI 2.0, you now have the option of using cheap players that just pass on the data unaltered to the display or an external video processor.
Does not matter, if it's 24fps or not. 4K material, most of which will be at 24fps is going to require HDCP 2.2 to get a picture. Older GPU are not going to work for 4K into the new displays with current version Display Port. The 60Hz is irrelevant really if you can not even get a picture to show at any frame rate for 4K material. Because HDCP has been "cracked" the new sets require HDCP 2.2 to display any 4K material. It's backwards compatible with HDMI 1.4 so you will still be able to display lower resolution material.
There's no reason that DisplayPort cannot be updated to support HDCP 2.2 as well. But HDCP doesn't seem like a big problem. I already use Media Center for all my video playback, so I don't have to worry about HDCP at all.
HDCP only matters for players like PowerDVD and stand-alone hardware.