The Milky Way done Minecraft style, eh? I'd imagine it as something really subtle appearing in the skybox during nighttime. Of course being slightly more pronounced when there's minimal to no atmosphere around. I could definitely think about it.
Also, the Sun and the Moon seen in the Overworld's skybox appears to be using a blending mode known as "Screen", which typically creates gradual transparency for individual pixels depending on how dark they are. I'd assume it's just meant as a simple way of emulating atmospheric haze during twilight. In the vanilla game the stars and the Moon never overlaps eachother, so that method makes sense there.
Given lunar phases has been mentioned (and a subject of previous discussion), I'd imagine it would be pretty nice if it took on a more realistic approach. It has actually been done before with the
Moon Mod, which I think is really cool:
I consider it has potential and would be a nice (and possibly optional to work around eventual conflicts with other mods) feature in Galacticraft rather than just having the Moon otherwise orbiting the Overworld's second Lagrangian point.
Eitherway it's tied to the concept of objects moving independently on extraterrestrial skies. Just imagine seeing Phobos speeding across the Martian sky for example.