Doesn't the Pixel Camera Services app bring these features to the API? (I am entirely in the dark in this topic, so this might be completely unrelated but looks like it has the goods in it)
Pixel Camera Services is a system component that brings Pixel Camera features like Night Sight to some 3rd party apps that you’ve granted permission to use your camera. This component is pre-installed on your device and should be kept up to date to ensure you have the latest image processing updates and other bug fixes.
I have it installed, it's modest in size (50MB) and doesn't even need Network permission, only declares 6 permissions in total (Read GSF, access network state, get package size, wake lock, camera, sensors), and in the screenshots it shows Night Sight in a 3rd-party camera app. Not sure if any work is needed to be done from GOS side, I will test out if it works in GOS Camera later today
Edit: if it does turn out to implement night sight, it might be a good idea to put it in the Apps repo client so it can be auto-updated with the rest of proprietary Google apps and easily installed for new users that want Night Sight. Of course some people don't want any proprietary Google tech but I see no risk in this as it literally can't talk to the network