I'd be curious how this handles all the posix cases not well suited to object storage.

Renaming a folder than has a million files/folders inside is a single operation in SFTP, but 2 million operations on S3.

Does it handle writing at arbitrary offsets within a file? Does it download the file first then let you start writing?

What about just writing a few bytes at the beginning of a large existing file and then closing your SFTP handle?

How about 2 users accessing same file via SFTP at the same time?