All I have to say here: there’s an advantage here that wxWidgets brings me: one can hope that the wxCocoa port of wxWidgets will step up to the plate. If it does (and I’ll probably pitch in here), then I just recompile my wxWidgets apps with wxCocoa, and I’ve made a major shift already. No rewriting all of my view (or controller) code, just recompile the underlaying library. Since wxWidgets is an abstraction, it just abstracted the API change away from me.
The only thing I would need to rework in my apps would be the places where I’ve called Carbon routines directly to provide Mac OS specific features, or where I’ve modified wxWidgets and now need to rewrite my modifications.