I also think about it. The probleme is Blossom servers do not store file path nor file name but only hash. So we need somewhere a db that store the path to hash matchs.
I see 2 solutions:
Solution 1 is to create a centralized middle server that expose a S3 api to the end user (rclone will talk to this server) and this server will process the user request using nostr and blossom.
Solution 2 is to create a dedicated rclone remote for nostr + a new NIP to match the file path with the file hash.
I prefer the solution 2 but it's more complex to achieve. I will be happy to work on that project, I want it too !