I actually don't see how signing everything solves the problem of AI generated essays unless you build a submission system that doesn't allow copy/pasting over a certain amount or that somehow assesses whether or not the 2000 words it just received were actually written by the user holding the keys or not.

Signing just is a means of asserting an authority over an item and then tracking that item once it's in the chain. The original validity of the authority isn't guaranteed just because it's signed; that was a non-trivial part of the debate over NFTs, wasn't it?

So I don't think signing really proves anything about the authorship or authority over the content written, it just tracks the content. The author's example that you can know they're the one who posted it doesn't really have anything to do with generated reports, and it doesn't even prove that they were the ones who uploaded the content any more than a classic blog with a username/password system. It just means that someone with access to the keys to upload provided content, not _who_ uploaded it. It's presumed it's the author as hopefully they kept their secrets safe, but that's not a guarantee.