Heres a stupid question, why not create another nip that allows a note to reference a file by secure hash, and anyone can add more uris to that particular file hash, and all the relay provides is a list of olaces to find the content. The clients search for a link to that hash from any relay until it finds one that contains a file that matches the hash. this way data can be deduplicated but in a decentralized way, and stale links can be updated continually through new posts and uploads.