Dohohoho, look at what I predicted!
The music for that round is going to be fantastic, I can already tell.
NOT necessarily. The platform stage itself may have been from Good Egg Galaxy. But how do we know it's still IN Good Egg galaxy?
Look at the right side of the image. There's 2 boss planets from SMG; the tree-planet where you fight the Monty Mole general, and (what I think is) the lava pool planet where you fight King Kalimari. Both of them aren't from Good Egg galaxy to my knowledge. The stage might just be a compilation of planets from various Mario galaxies.
ALSO,
I'm unhappy that it isn't the Comet Observatory stage we're getting.