Great stuff Notminor!
You look to have covered the core stuff well, due to the fast speed of things its a bit difficult to tell some aspects and possible improvements, I was going to suggest handling the constellations and moon as well as the sun based on lat/long but I noticed constellations in the list at one point I just don’t think you touched on it, or showed a night sky, possibly because you haven’t had time to work on that yet.
What are you thoughts for the AI weather? Would it be driving primary global motivators which would then be driving local/regional weather values? While having the weather being fed by real time data is a great way to lessen the complexity of the global forces driving local patterns it does limit the ability for events taken place in a world to provide feedback into the global system AI. It also becomes less relevant or useful if you no longer want to represent current earth or its conditions. One approach might be to use current weather data as seeds for driving the AI/unique weather events, that way there is still structure and continuity but the result doesn’t mirror the real world patterns directly and you can still override the results with specific events like a volcano eruption, forest fires, or grand magic! I think your choice of doing the AI for global systems first and hooking in weather data later is the right way to approach it. Best of both worlds that way.
One other thing to note, it looked like the snow was forming and melting around the 15 degree Celsius mark, that’s a bit too warm for that and you wouldn’t see that happening unless there is a severe northerly from the arctic blowing in a cold front, you will generally be closer to the 0 degree mark for snow to be falling, and your accumulation will be based on a number of other factors like ground temperature (melts fast in fall before permafrost sets in, slow in spring etc), sunlight will have a varying effect on thawing rates based on angle but that might be too much to try to factor in there, but perhaps factoring in the relative cloudiness/sunlight the ground is receiving could be a workable factor in the process. Generally though the mass accumulations that occur as you have shown them around wind breaking objects and undulations in the terrain and these will retain themselves longer then lighter amounts of snow in open areas which it actually looked like they were doing at the end of the video, which made it quite realistic looking to this Canadian, well done!
The last suggestion I would make in regards to the snow is its ability and variety to reflect sunlight to the point where it can sometimes even be blindingly bright, it appeared a bit too dull and while it worked for the cloudy days it seemed off for any weather other then full clouds. On a clear sunny day in the winter it can be vary apparent depending on the formation or snow, whether hard wind-packed or soft freshly fallen etc. But generally it all shines in the light to some degree.
That’s about all I can think of right now, except to say I am blown away by how much you’ve covered and how well it looks! Keep up the great work I’ll be very interested in seeing this released.