For home or SOHO users it might be nice to have:

* a new type of /system logging action, something like "led"
* a new type of firewall action (or maybe a led parameter), so that a firewall rule would trigger...
* a new type of led type, sys-alert

So I could have the red led in the routers blinking for some kinds of unusual activity like new incoming connections in non-service ports.
It could also be linked with critical log messages, so that if the led blinks more than usual you know if might be a good idea to take a look.

Nothing that can't be attained with a remote log server or a script + blink a bit more clumsily, but handy for a travel router or a home one...
I also see that the name and type of leds is not consistent between models, and also location or type of led:
* /blink on hAP ac acts on the SFP one, not very visible, only wireless and sfp can be configured.
* on hAP ac lite all leds can be managed, but "usr" one (blink) is in the back and barely visible