I think it would be pretty cool (if Sonic is confirmed) that Tales' airplane was a stage. And it flies around, and it acts like a real airplane also. So, if all characters are on one side of the plane, the plane will tilt, and if it is raining, your character might slip off the stage. The stage will also have weather effect (i.e. Sunny, Rainy, etc.) The plane will also end up doing backflips and stuff, and the game will also warn you beforehand that it is about to do a backflip. In order to prevent your character from falling, you'll have to grab onto handles that are on the side of the stage.
Another possible stage could be King K. Rool's ship from DKC or any other Donkey Kong game. So, basically, you're on the ship, and it is going out at sea (obviously). There are a few trap doors, but they don't lead to your doom, instead you fall inside the ship, and the only way you'll be able to see the character is through the ship's windows.(or some other way). King K. Rool might make cameo appearances and just shoot Cannonballs at you, which will lead to more holes in the ground, but will eventually repair themselves, And then after a while the ship will crash so now you all go underwater, and well, the fight still carries on! Then there's this stage's hazards, which include Sharks, eels, etc.
Sounds stupid, but it's just some wacky ideas I had.