How to move around the content isn't really a problem I'm trying to address. As far as I can tell it's a solved one, has been since Napster. Different users like to manage their media differently, I'm not going to tell them how to do that.
Same thing for managing user identity. Whether you want to build an organization around that problem or slap together a CLI and let the users fend for themselves, again not something I'm trying to weigh in on.
These are app-level decisions, not a protocol ones. And neither of them really lend themselves to on-chain solutions.
The unsolved problem I see here is that you've got a community of users, all with identical copies of a file, and they want to build consensus on how that file should "cite its sources". In the case of music, that's a bunch of fans wanting to pay the musicians, but it's structurally the same as if you're trying to give feedback to authors of a paper or claim that researcher X found vulnerability Y in code Z: you're building consensus on a directed graph between datasets and actors such that other actors have something to reference when they communicate (or send payments) to each other about those things.
That's the only part of the problem that's likely to come under attack by incumbents, so it's the only part you need a ruleset and computational verification for. Everything else can be handled "the normal way", by appealing to the good behavior of the incumbents.
People (e.g. Sony) are going to try to get paid for music they never played. People are going to take credit for research they didn't do (or did poorly). People are going to try to misrepresent the trustworthiness of things that they built and want to charge you for.
You can't put that on AWS because nothing on AWS is more trustworthy than its least trustworthy admin. You can't leave it to the courts because only the powerful can use the courts to their advantage, for the rest of us they only serve as a system for mutually assured destruction.
Which people get credit for which data is too contentious of a topic to trust to the hands of people who have pinky promised not to use it in their power games. If it weren't, there'd be no reason for Subvert to exist in the first place. I hope they can manage it by just being very careful about how they allocate trust among their owners, but history has given us centuries worth of reasons to be skeptical.
Meanwhile, other data that the powerful would prefer to tamper with remains intact in the various blockchains that protect it. The rules continue to be followed. There are a lot of problems with that space, especially at the interface between the rules-governed parts and the pinky-promise parts, but we've only been chipping away at those problems for decades. They feel a lot more tractable than anything involving the insufficiencies of the law.