Stages:
Mario: The Faceship. Fairly obvious stuff; could maybe function as a Brinstar Depths kind of stage, with the ship flying and rotating in flight. Plenty of choices for hazards too; comets, hungry Lumas, all sort of stuff.
Zelda: The Sand Sea. A bunch of platforms suspended over the sand, which would function as a KO. The Sand Ship will occasionally sail past and transform bits of the sand into water, which could be swum in to save yourself. Extra platforms could appear or disappear depending on where the ship is.
Wii ____ series: Wuhu Island. Gets the Isle Delfino treatment; floating platforms taking the fight across the island. The town, the volcano, the golf course etc. I'll be amazed if this doesn't happen.
Pokemon: N's Castle. A Spear Pillar type stage, only with both Reshiram and Zekrom fighting in the background at the same time, with occasional blasts of electricity and fire thrown across the stage.
Professor Layton: The Moving Fortress. This is, of course, dependent on Layton being in the game. The giant robot from the end of The Unwound Future, with explosions and debris, with the Laytonmobile occasionally appearing as a platform.
Xenoblade: The Sororal Statues. Fairly basic stage layout set on top of the statues. Features a cosmetic change for the night time, complete with music.
(NOTE: This probably should be Gaur Plains as the game's most iconic location, but I can't really figure out how it would work without selling the location short or being derivative).
Zelda: The Train's Flatbed. Spirit Tracks stage. Fighting on top of the train as it goes around the overworld, with snowball-throwing snowmen, floaty underwater bits and steep volcano climbs. New platforms and battling terrain picked up by the train as it goes round.
