I stated how it would affect gameplay on the first post?...
It's mostly for the new players + people who probably haven't searched all of Graal's areas. Won't be dark clouds either, I feel like the current clouds would be the best option to cover most of the map (When you start a new account).
That being said.
I don't have the slightest idea on how hard it could be to implement.
BUT, from the looks of it, it might be something that would take up space in cache for having the images saved of where you have been on your map, instead of a set image.
Because I think in minecraft, the sky pretty much places the blocks onto the map like a picture from above.
The effect would be adventure, like I said, think of this update as if you were a new player starting out. You have no idea what lies beyond that forest, you will have to travel across lands to unravel those mysteries.
Changing gameplay? For beginners, a lot. As for the new players, every time a new area is added (Snowtown, Deadwood, York, Destiny), they can go around the world and explore that new area. Could also be used for achievements "Christopher Columbus" (Example).