Great quiz! I think miiverse is the only real reason why every stage isnt returning. I personally want Pac-Maze, Rainbow Road, and Poké Floats. I would like to see most of them return, however, even though I doubt it will happen.
Pictochat, Sector Z and Planet Zebes are also pretty good reasons why not every stage is returning. They all have modern counterparts. On an unrelated note, writing this comment I remembered 2 more answers that I forgot lol.
Except that Sector Z is better than Corneria. Not in terms of visuals or music, but to actually play on. And the new My Music rules would've solved one of the only two problems.
I’m not saying that I like the newer stages more, I’m just saying that the reason the older ones aren’t returning is because they have the newer versions.