Small weite up for you: exfat is only supported, after you install an exfat Update. This happens while the exfat sd is inserted and you Update the console.
Elseways use fat32 or install the Update manually.
Before that happens, the fw need to be published. And if possible, then it's something very long down the Riad, as it is t top priority.
So no matter how good the idea night be, I don't think we will see it anytime soon or ever.
@Xdqwerty, Osu! Tatakae! Ouendan! is the Japanese version of the game, different settings/characters/songs but otherwise identical mechanics. I played that before I knew about Elite Beat Agents lol. Both fantastic games https://en.wikipedia.org/wiki/Osu!_Tatakae!_Ouendan