FWIW I've often thought that it would be very useful to create a utility that provides an interactive text-based dialog with the developer to build prototypes for this. wxGlade was extremely frustrating (which is probably why people use the commercial version).
There once was an AI system (I forget the name - something treasury I think) that used ascii art drawings to map rooms and tell the system where the bed is, etc. in order to describe the plot of a story. I've thought ascii art (or more modern) representations might be interesting ways to quickly block out GUI layouts, and (though it shouldn't be) be a lot faster than frustrating wxGlade. FWIW.