Since Hive with their block party is able to play other music in game, maybe this is possible too? Maybe something like those "if Minecraft was a rhythm game" videos or something where you have to hit with your sword to the beat? And as for music, the Vocaloid and BMS spheres have many kind artists willing to provide! Make it like Parkour where it's per level maybe? I dunno, it's up to you how yall will implement it. All I know is that it will make rhythm gamer YouTubers flock to your server and expand your horizons. The technical stuff behind the scenes might be hard though. Maybe mods can help?
Thank you for all the hard work you've done. We'll never forget you.