From the discussion at

https://www.reddit.com/r/crypto/comments/61zupq/amazon_drive...

I learned that Amazon Drive is a service that provides unlimited storage for a fixed cost, and that various applications, including rclone, use it for an application that I would expect (as a developer) to use S3 for, and therefore to charge my users per amount of data stored. (Amazon Drive is not part of AWS, I believe.)

I am not extremely surprised that the terms of service of Amazon Drive make it hard to build a compliant application like what rclone is trying to build. I'd expect they can do this with S3 straightforwardly -- at the expense of users needing to spend O(n) instead of O(1) on their data.