This is a very interesting idea. However details should be hammered out before it becomes a real proposal. It sounds like from another comment that you are talking to the team behind the scenes.

I admit I probably wouldn't buy music as it's not my thing. But I know that people buy "skins" in this and other games so it wouldn't surprize me if there was a market for it.

I know the current stuff is AI though and I wonder about the balance between people putting a prompt into AI verses people taking the time to compose, sing and play an instrument. Or even a combo. such as someone coming up with Lyrics but letting AI figure out the rest. I personally know an artiest (she draws) who HATES AI with a passion because it causes "real" artests to not be hired. But this feels more fun.
If this is kept at a fun level with a bit of "beer money" and/or - "pay with packs" involved I think it could be pretty fun.

If it's Serious though - like if people expect to make a decent amount of money then IMHO it should only be open to non-AI artists. A lot to think about.
BTW these thoughts are based on the complexity and the multiple ideas you present in this post. I don't expect all to be implemented but it would be fun to see some of it. :)

#2 cents

-- LadySharon