Seems useful for s3 buckets. I suppose a script that watches for new objects, calculates its sha256 and stores that in a DB, then checks for duplicate hashes would be a fairly trivial task. Though s3 doesn’t support symbolic links so accounting would need to be handled by server side code.
I don't think it's very useful but there's already a checksum in the meta data of an S3 object: https://docs.aws.amazon.com/AmazonS3/latest/API/API_Object.h...
It might be better to keep an index of paths to checksums and use the checksum as object key in S3.
I'm not sure what you like to achieve but if you use restic with S3 as a backend you can achieve much better deduplicate and compression.
While the idea of data-deduplication does apply everywhere, this specifically depends on the APFS CoW data feature, so it's not applicable outside of macOS (or APFS Volumes)