The thing with bumper cars is they don't require a lot of infrastructure and a professional staff of skaters such as the ice rink does. It appears they will use the existing Seaplex floor with nothing special involved. I suspect the cars are battery powered with computer controlled governors to prevent people from going crazy in them. If the bumper cars don't pan out they can just remove the cars. It was a comparatively inexpensive thing to put on the Quantum.
Wasn't the original Studio B idea to have passengers be able to make their own videos and song recordings outside the ice rink? I forget now since it is really just a sports bar most of the time on the ships such as the Freedom class.