Did you consider PyQT as an alternative? Riverbank Computing has done a fantastic job maintaining python wrappers for Qt and likewise it also generates native windows for each platform. There is a build tool called PyQt Deploy that helps package up the app for various platforms (I have not used it however)
The python documentation for pyqt is pretty lacking IMHO but referencing the official qt.io website makes developing a breeze as the PyQt wrapper is almost identical every time (some variations exist when you run into pointers to pointers and such).
I did indirectly because I've used pyqt before. It's okay, and does address the concern of stability, likely future proofness, etc. However, it's more complex for sure, and I recall it not feeling super Pythonic or intuitive. I also don't think QT generates *actual* native widgets, just that it draws widgets on each platform that *look* native. We've long been beat up by the blind community for not having native widgets on Windows, which causes their screen readers to see a blank window. This is not a primary goal here, but it certainly seems like a nice thing, especially since even Windows' look and feel has changed over time.
I can say that the wx-based MacOS app is worlds better than GTK3 using Cocoa drawing and emulating the native Mac widgets.
--Dan