Write your local congressman (depending on where you live this position may have a different name). Go to the local political party of your choice and make it known that this is an important issue. Remember votes are more important than money in politics - money can buy votes but only when voters don't care about issues. So if many many people make this an issue things will change.

If you want your server to stay secure, then that is not really an option. Copyright is not the thing that is stopping your suggestion from happening.

Just have an oauth flow to grant permission to the store to upload movies. It would absolutely be possible to implement securely.

Implementation details. At checkout put in a public key or something similar, at the receiving end accept a dialog to accept film <x> from <y> movie buying site.

Signed URLs are a thing.

Copyright itself isn't what's stopping that, but the legal apparatuses and laws surrounding the distribution of digital copyrighted information and the industry protectionism that spawned said laws and legal apparatuses is what's stopping it.

This is actually not a bad idea.