I've got a basic workflow working with per-user libraries.
As a user, you can create one or many libraries. A library can be private, public or restricted to users from the same instance (you can share them directly with specific users as well).
You can upload tracks to your libraries without any permissions (as long as you respect your quota).
And you can listen tracks from all the libraries you have access to.
There are still a lot of things to do before this is ready, but the current workflow is actually much, much more simpler to deal with and removes the need for:
- instance level library
- upload permission management
- music requests
I also find the import process faster and cleaner now.