Hm, this would indeed be an interesting feature to have. I would love if i.e screen brightness automatically dimmed based on time of the day and/or other criteria (same with keyboard backlit). I suggest youopen an issue and prepend "[Feature request]" to it and explain what you would like.

In meantime, there's a GNOME Extension "Dim on Battery Power" which I used for this purpose. But unfortunately it hasn't been updated to support latest version of GNOME.

Regarding keyboard backlight, I keep it off, and on X1 Carbon it's one shortcut away from being turned on "fn + space".