it's sometimes very helpful to think of filesystems as a streamable blob store with a hierarchical key

That's one valid perspective. But don't forget that you can also seek and mmap etc. And hard-links are a thing, too.

Things like fuse also show that it's easy to view other databases as filesystems, too. As a silly example, you can 'explode' /etc/passwd into individual files per entry. Or you could expose even a relational database as a filesystem.

For the latter, you could do something simple and expose tables as directories and rows as files. Or you could do something dynamic, and eg represent (read-only or idempotent) queries as file-names, and their results as file contents.

That wouldn't be so much a traditional filesystem, but would be accessible via a filesystem interface.

I hear AWS DynamoDB is basically just a "key value store interface" to S3 file storage.