I know we're off the stages topic at this point, but seeing all the other replies with obvious stages I missed just drives home how utterly amazing the fact is that we're getting practically every stage back. At the moment, that's really as exciting as the roster to me.
While I'm at it, I imagine this was brought up a couple months ago (for music-related reasons), but imagine how amazing the city from Air Ride's City Trial would be as a new gimmick-based / travelling stage. You could fly around the city, which has enough cool set pieces at it is, but you could also integrate picking up stat boosts akin to the ones in City Trial / Smash Run (Jump, Offense, Defense, Speed...) to power up your character's stats over a match, and lose some on hitting a stage hazard or losing a stock.
Don't think it'd be terribly likely even if there are five more stages to reveal, but a guy can dream.