Here is an (edited) conversation I had over chat with a friend today.
The point of this conversation is that I'm exploring the idea that what Agile is missing is front loaded change feedback. Something along the lines of, "Ok, we can do that but it'll cost you $5." The current model works like this, "OK, we did the work, that was days/weeks ago, and it cost you $5."
This is not about controlling change or costs. It's about visibility.