I will check if I can it get running on my old Acer, at leat I have a ton of unused LED on it.
And can't one use the background light of a keyboard as a notification light?
And can't one use the background light of a keyboard as a notification light?
You can use anything that is exposed by the Linux kernel under /sys/class/leds/*. This includes the keyboard backlight of ThinkPads. As for other vendors, it depends on whether the keyboard backlight (or any other LED) can be controlled in software, and if so whether it is supported by any kernel driver.