For me, setting the LED to always on (it was like it by default) works fine even now, because I built OpenWRT from "20190525_aircube_led" branch in your repository.
One question is bothering me. I'm planning to buy AirCube ISP AC. Since this router is using exactly the same firmware file as AirCube ISP, then also the same OpenWRT image should work on AC version. (Maybe except for 5GHz radio, but I can add support for this by simply installing packages that are providing drivers for it). Am I right?