If they have Mario Party 9 music, maybe they'll have music from older Mario Parties? I mean I know it's a Mario Kart stage and not Mario Party, and that was based off a song from Double Dash, but if they did I'd really like
Let's Get a Move On from Mario Party 3,
Going Somewhere from Mario Party 2,
the opening from Mario Party 1, or
Valuable Treasure/
How to Play from Mario Party 4 (more than one of these would be a lot I know but let me dream).
Also, I noticed something in the screenshot for the My Music page for Mushroom Kingdom U:
(I think Ground Theme/Underground theme is the one that played in the E3 Demo and is in the 3DS version, and SMB Medley might be from Brawl) Didn't the Lost Levels have the exact same music as Super Mario Bros? I'm really hoping this is a translation error and that's really a Super Mario Bros 2/USA/Doki Doki Panic medley or else we'll have at least 3 separate remixes of the same theme for the same stage, which is really quite a waste when you think about the backlog of music they had to work with, most of which hasn't even been remixed once for Smash. If there's no more music left to be unlocked for this stage and 9 is the final number, and they use the Super Mario Bros 3 Medley from the 3DS version and the original NSMB2 overworld music that was in the 50 Facts Direct, that means only 2 music pieces left
and they'll probably just be other remixes of the SMB theme. Hopefully they won't disappoint!