@Powerstars: sure, go right on ahead.
And I'm feeling like posting some stage ideas.
[COLLAPSE="Some stage ideas (contain spoilers for other games)"]
Rosalina's Comet Observatory (Super Mario Galaxy + Galaxy 2)
Would travel around galaxies from both Galaxy games. Starship Mario, the Toad Brigade, Rosalina and the Lumas would cameo here.
Rainbow Road (Mario Kart series)
Would have an original layout and borrow elements from all Rainbow Roads, including: rainbow Thwomps from SNES, the moon from MK7 version, have elements from Super Mario Galaxy like the Wii version (Star Bits and the star launcher) or rainbow colored figures of Mario characters (like in the Double Dash version, I think...). The stage would be like Mute City.
Mario Toy Company (Mario vs. Donkey Kong)
Set in city rooftops with the Toy Compay building and Mini Mario theme parks seen in the background, making this a sort of successor to 64's Saffron City and Melee's Fourside.
One of the buildings would spawn Mini Marios, Mini Peaches, Mini Toads, Mini DKs and Mini Paulines, which the players could grab and use as items until they break.
Sometimes, a mechanical Donkey Kong would appear riding on a platform reminiscent of the DK arcade game's (see 75m in Brawl), throwing barrels, bricks and all sorts of junk at the players. This obstacle would be warned by the classic DK intro tune, also present in 75m in Brawl.
In the background, posters featuring pre-Rare DK characters would appear, such as Stanley, DK Jr. and Pauline. The three Toads (one red, one blue and one yellow) proeminent in the MvsDK series could be seen operating a crane in a constuction set in the background.
Return to Dream Land (Kirby series)
Mostly inspired in the Wii Kirby game, this stage would be a combination of many settings. Like 64's Dream Land and Melee's Green Greens, expect Whispy Woods, a rainbow and star shaped objects, unlike the mentioned stages, this wouldn't take on a floating island, rather being on land, having walk off KO zones. The sun and moon bosses (can't remember their names) would switch the stage from day to night and from night to day as an aesthetic feature.
Angel Land's Divine Ride (Kid Icarus series)
Taking place atop a marble platform with glowing symbols, this stage would take the players to many landscapes from the Kid Icarus series including Skyworld (with Palutena's Temple visible in the background), Underworld, Overworld (could be a human town modeled after typical Ancient Greek towns), Temple Ruins (place where Pit and Dark Pit fight in Uprising), the Space-Pirate Ship, the Labyrinth of Deceit, the Thunder Cloud Temple, the Lightning Chariot Base, an assortment of Aurum islands and ships, the Chaos Vortex and Dyntos's Workshop.[/COLLAPSE]