Eh, I don't have pictures to illustrate my choices, but excluding any stage we've seen until now...
1) Movie 9 Tenkaichi Budokai
With those platforms at different heights and water, it might be interesting.
Would love a tournament option based on this movie: ring-out water, big melee in introduction to decide who will be an actual contestant and finale as a time-attack against three other contestants.
2) Babidi's spaceship (just like
DragonBoxZTheMovies 
)
It was already there on Super NES and is a place you can truly identify as a "Majin Boo era only" kind of place.
Starting in a small room, it could include breakable floors, with four or five breakable floors, extending the vertical space as the fight goes on.
3) Kaio's planet (again, thanks for the idea
DragonBoxZTheMovies )
That small planet could be an interesting and mind-disturbing place to fight if the planet is used as the ground area (instead of being in free-flight with the planet just being an obstacle), given the speed you can go all the way around.
It's an iconic place, but it would also bring some new strategic elements, like trying to take on your opponent from behind, or sides: getting away would quickly mean getting closer on the other side of the planet!
