HDMI 2.0b has everything what we need for 24fps content, which is the current frame rate used for shooting feature movies. Studios can remaster all past 24fps movies at UHD, BT.2020 ( P3 inside ),10/12/16 bit, 4:4:4 color sampling and they can do that with HDR10 ( static ) or Dolby Vision ( dynamic ). HDMI 2.0b supports also HLG format, suited for broadcasting.
The problem with HDMI 2.0b is with delivering 50/60/120fps at 4k, BT.2020, 4k, 10/12/16-bit per color, 4:4:4, HDR ( both static or dynamic ). HDMI 2.0b does not support dynamic HDR10. Only Dolby Vision offers this capability, because metadata encoding works differently and it doesnt rely on HDMI standard. Second problem is with the ecosystem. HDMI 2.0b has limited bandwith for audio and video, so PQ is compromised especially with 50/60fps and future 120 fps content.
HDMI 2.1 offers finally a proper connectivity to make shooting and distributing very high quality content in the future possible. That is: 120fps BT.2020 ( also as a container ), 4k/8k, 10/12/16-bit per color, 4:4:4 sampling, HDR ( both static or dynamic ).
I personally look forward how HDMI 2.1 impacts Ultra HD blu-ray specifications.