I am basically talking about the Instrument system from ArcheAge.
The system basically worked like this: You could get blank music sheets and write down notes on them. And if you then used the music sheet, your character would use its equiped instrument and play what was on the used music sheet.
Depending on the rarity of it, yu could write more notes down. Every Character could do this and it was really popular in my guild, we even had little concerts and a small group even started making their own songs, instead of copying existing ones.
I would love to see such a system in Ashes of Creation, I think it would really add to feeling at home in the world, when you could make your own music.
Heres a Video, not from me, not my Guild, but a good example of what the music system in ArcheAge was capable of.
https://www.youtube.com/watch?v=tw--Ac34gbM
https://www.youtube.com/watch?v=_9XonwCemQs