At the moment, as I said, this is just a colour test (mainly to make sure I could do the aurora the way I wanted). The end thing will (hopefully) look a bazillion times nicer than that and perhaps have a break in the ice with bergs in it and other things to make it look nice.
I wanted to keep it as a clear night (the aurora wouldn't be visible otherwise). I plan to make the lights MASSIVE. Having seen the Australis myself (I was disappointed not to have caught the Borealis whilst I was in North America - there were only two clear nights in the three weeks I was in Ottawa ), I want to do them justice. Plus I like stars, and would like to look at putting some southern hemisphere constellations in (it's now Antarctic ). I'm envisaging the aurora being the main eye-catching-moving-thing-standout-point much as the meteor will be in my volcano one (except HUGE).
I'd like to have snow falling, but I feel that would be better as foreground billboard type stuff, and I'm not 100% sure how all that works at this particular point in time (at the moment, I've been having clipping issues with really close billboards).
I'm not sure about how to go about making billboard elements move along a path like you're suggesting. I don't think it's possible with the current mechanic.
Similarly, with seals and the like (since when to seahorses come out of the water? ), I don't know if there's a way I could come up with animation that I would be happy with. I do have sketches for a beach environment that I wanted to have leaping dolphins in.
Edit: I'm also planning on making my cartesian-spherical coordinates (or "plane generator", which sounds more impressive) available to anyone who wants to play around as well as any other bits in pieces I put together whilst I'm working on these (and maybe update the documentation a bit). Who knows, maybe I'll get motivated enough to write a point and click environment creation GUI.