Hi, Rich. I wrote something similar but more barebones, called deps, for folks like me who prefer a more manual process. deps is trivial: It just outputs each linked library and the extension that provides it, in table format (similar to readelf -d output). It's then up to the person creating the extension to use the data in the table to create a recursive .dep file (e.g., using Brian Smith's deptree script).
I hope you don't mind me attaching deps and deptree here. I thought it might be nice for this thread to be one-stop shopping for anyone looking for this kind of thing.