By allowing resale of digital copies outside of platforms all you get is essentially the complete repeal of intellectual property rights for digital media.
I think as a compromise I'd be okay with some kind of license database (maybe blockchain-based, maybe not) that keeps track of who owns a legal copy of what. People reselling digital copies of copyrighted material would have to transfer ownership of that license to prove they're conducting legit business and not just minting new copies out of thin air.