sure, one could make storage/retrieval authenticated and end up with something like dropbox; files are encrypted in transport but the server can read them

the lack of partial updates (as they would change the SHA256 hash) would bring some inefficiency for cloud uses compared to other network file protocols

the E2EE layer exists on top of that, and that paper is about how it's very hard to achieve without leaks of some kind, so that's where the challenge starts 😀