Really like this, shows off the models very well, and an interesting area of TG to master, ie the rays and atmosphere.
If I was working on this program, which probably thankfully I'm not, I'd like to suggest a distance fall off setting on atmosphere samples, or even use a distance shader attached to atmosphere quality. I don't think that would be too hard to implement, and would help render times exponentially towards the horizon, there's no need to put quality into distance, you just don't see it.