Along the code generation line of thinking, Laetitia Duby (working with Rafael Calvo) has made a good start on extending ArgoUML to turn UML-like diagrams into OpenACS database schemas and tcl/adp pairs.
You can read about the project and download the current code here:
http://www.weg.ee.usyd.edu.au/people/laetitia/
I'm imagining some kind of base package meta-design that you could open in a tool like this, play around with the user interaction by clicking and dragging objects (you could easily do this with the client there), have it generate the bulk of code for you and tidy it up by hand.
It's not quite there yet - but tantalisingly close.
