Most modern backend is building consistent distributed state machines, you need to cover all the edge cases, deal with concurrency, different clients/contracts etc. I would say getting BE right (beyond simple CRUD) is going to be hard for LLM simply because the context is usually wider and hard to compress/isolate.

Seeing the kind of complexity that agents (not standalone llm) are able to navigate - I can only start to believe - just a matter of time it can do all kinds of programming, including state of the art backend programming - even writing a database on its own - good thing with backend is its easily testable and if there is documentation that a developer can read and comprehend - an llm/agent would be able to do that - not very far from today.