I've taken the plunge and started working on a new backend for McCLIM using Graphic-Forms as the substrate. Thus, the result will be a native Win32 backend. Realistically, some time will have to pass before I've got enough functionality working that at least the standard demos can run. It's OK to make quick-and-dirty hacks just to see something pop up on the screen, but if I'm going to propose adding this backend to McCLIM for real at some point, then it needs to play by the rules.
There are plenty of good reasons to take this project on, but for me the most compelling argument is that CLIM represents a much higher-level way of thinking about GUI building. Since I think of myself as somewhat of a specialist in GUI development, this is very important. After I've climbed the somewhat steep learning curve, digesting new concepts along the way (like what the heck `flipping ink' is all about), I'll be that much stronger in my GUI-fu. I can take some of these concepts back to my design of Graphic-Forms -- not necessarily with the intention of directly incorporating CLIM concepts like presentation types, but as a way to take a fresh look at the services that GF provides. After all, GF is itself an abstraction layer over the Win32 User/GDI APIs and does some translation of raw Win32 concepts to Lisp-y abstractions.
A secondary benefit of this will be more code that uses Graphic-Forms, and maybe more users (albeit indirectly).
By the way -- hooray for open-source and Lisp and learning new things and having the ability to spend as much time as I want on this stuff!