Anyone who wants to try this and is using Magisk, I created a Module. If it gets traction I'll submit it to the Magisk repository. For now you can just download the attached zip and install using the Modules tab in Magisk Manager.
NOTE: This requires Magisk 14.2 (beta) or newer, available at: https://xdaforums.com/apps/magisk/beta-magisk-v13-0-0980cb6-t3618589
I mostly did this to experiment with Magisk, so far I don't notice any difference with my Nexus 6 running OmniROM 7.1.2.
Source code is here: https://github.com/TonyApuzzo/assertive-display
Module works for my nexus 6.. adaptive brightness changes instantly when in sunlight
Sent from my Nexus 6 using XDA Labs