This would be nice, and I've thought about this before as someone who manages one of said music groups.
During the 2019 Christmas (aka Starlight) event, there was even a little minigame where your character acted as a conductor. So the animation EXISTS, we just need it as an emote.
At the time, though, bard groups needed someone to help keep them in sync... basically a conductor. They'd do this with a chat message to signal when to start. When ensemble mode was added, we got a way easier way to handle this. So groups actually needing a conductor is rarer now, but it would still be nice for bard groups.