The only reason I still haven't moved from gammastep is it's ability to dim the screen backlight at night. Is it possible to add this feature to this project?
gammastep does not adjust screen backlight to my knowledge. It desaturates colors on the screen to make it look dimmer, significantly reducing the effective dynamic range of the monitor (which is already reduced a bit by the blue light filter). This is a major hack that I would not want to use myself. For trying out proper sun-tracking backlight control, I think the best starting point would just be to fork wlsunset and replace all the wayland code with backlight updates (/sys/class/backlight/*/brightness for now as DRM has yet to absorb backlight control), at least for laptop screens. It should be noted that the required backlight is not really tied to the phase of the sun, but is rather tied to the amount of ambient light. Personally I use a small script that runs when I start sway and every time the lid is opened to set the brightness based on a random heuristic I made (I was too lazy to use my ambient light sensor), as my only concern is spontaneous blinding when opening my laptop at night after using it during the day.