Smash could do with a good beat-em-up elevator stage. Not a scrolling stage, just something with a background that moves up or down, perhaps it could have side platforms that scroll while the main part of the stage doesn't.
I know that you're probably picturing something that scrolls slowly, but man your idea made me realize how much I didn't know I wanted Terminal Velocity from Sonic Colors as a stage. Massive flippin' space elevator connecting Earth and
Doctor Eggman's Incredible Interstellar Amusement Park™, what's not to love? It was such a cool idea for a location even in its game of origin, it's practically guaranteed to stand out in Smash. Instead of, y'know.... more green hill....
I'm picturing the main platform rapidly descending as you see this massive space elevator looming in the background. I think it'd be really fun to be descending the entire time, but the main platform still slowly and dynamically moves around so you can see the scene from different angles (and so you're not looking at the same part of the elevator the entire time). Basically what Hollow Bastion does but a lot slower.
I definitely think the latter two camera shots could have an awesome "wow" factor, with Earth looming on the horizon in one, and Eggman's Park in the other. Also, you could literally just have the Terminal Velocity theme (as heard in the gameplay footage of the video) play on this stage and nothing else and I'd honestly not even care, it's such a banger track and suits the mood perfectly that I wouldn't need anything else.
(Man, like.... can we... can we please stop getting generic grasslands for stages and have stand-out moments from games turned into stages instead? Like I know I'm preaching to the choir at this point, but every time I see (or come up with) a new idea for a really cool stage I just end up even more dissatisfied with what we currently have and how utterly uninspired it is.)