If you try it out, let me know how well it works. So far I only had a chance to test it on a ThinkPad X230 and X250, and I would be interested to know how well it works on other models, potentially even with other vendors. Though, I haven't seen any non-ThinkPad laptop yet that has LEDs that can be controlled through the Linux kernel.
Also in case you are using Firefox on Debian/Ubuntu, note that blinklight requires at least Firefox 50, which is not yet in Debian stable/testing, but Firefox 52 can be installed from experimental.
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.