I would like a action to set keyboard backlight brightness to be added as-well as a new variable for keyboard brightness.
This should be achievable using the coreBrightness.framework that comes with macOS (sadly its incredibly undocumented).
I can link some github projects that has used coreBrightness to get and set the brightness level if necessary.
I would personally use this to create a controllerstrip button that toggles the backlight on or off.