The bulleted list of what constitutes “ideal” is missing one of the most important types of questions: questions that aren’t answered by the knowledge set, but which seem like they should/might be.

This is where RAG systems consistently fall down. The end user, by definition, doesn’t know what you’ve got in your data. They won’t ask questions carefully cherry-picked from it. They’ll ask questions they need to know the answer to, and more often than you think, those answers won’t be in your data. You absolutely must know how your system behaves when they do that.