Well, I decided to create a few SMG stages for Brawl... So I had two concepts.
The first one involved a sphere (circle, in 2D terms) that the characters would walk around, with no gravity pulling them off the surface (center of gravity at the core of the mini-planet?). Also, there was a tiny moon that orbited around the planet, with characters able to jump up onto it.
I figured it might be a little hard for the dev's to create, so instead I created and completed Concept #2.
I extended it during creation, but don't know if the length will suffice a four-player free-for-all. I can always add extra platforms though...
Oh, and there is a black hole underneath each grassy area. Anybody following SMG will know... its death, really.
EDIT: And four seconds after looking at it again, I think that it might need to be extended in height. Just so jumping into the "Gravity Twirl" by accident dosen't get annoying... Will change later, maybe.