There's a start-up called [Murfie][1] that is doing this with physical CDs - you mail in your discs and they do a digital rip of them, and allow you to sell the digital copy on their website. They retain the physical discs in their warehouse, which is kind of their "proof of ownership" for being able to transmit and manage the digital copies.

[1]: https://www.murfie.com/about_us