I'm curious, what would be the engineering challenges (either hardware or software) in making it dimmable substantially below 2500 lumens, so that it could continue to work as a primary light source when winding down after the sun goes down, rather than switching to other light sources capable of getting dimmer?

The manual version could be done with a plastic frame and some filters: https://us.rosco.com/en/products/catalog/roscolux