The problem isn't how bright should 1023 be. The problem is how bright should diffuse white be (aka graphics white or SDR white)? None of HDR10, HDR10+, or DoblyVision ever attemped to address that question. Which is a pretty important question to answer if you want to use HDR in a desktop / multi-window environment.
None of HDR10, HDR10+, or DolbyVision ever answered the question of how to adapt for varying ambient brightness levels, either, which is again a very important question to answer for portable devices like phones, tablets, and laptops.
