I agree that client requirement sculpting is a major issue. But I think if we could give them something like the kind of detailed 3d walkthrough that's possible

I agree that client requirement sculpting is a major issue. But I think if we could give them something like the kind of detailed 3d walkthrough that's possible now in architecture, for example, we could possibly also get them to agree that no significant changes will be made once they've signed off on the plan. I have no idea how this could actually be done though. So many of the implementation details are opaque to any non-technical client.