John,
You asked me this a few years ago, the answer is still 'no'.
I know there are many fans of IUP (there's also a module for Nim), but I'm not one of them. From a programmer's usage perspective, it's good. From an implementor's perspective, trying to bring a new base toolkit to it is an unending rabbit hole. There are far too many obfuscated layers to IUP that require unraveling.
In my opinion, there are too may GUI tool-kits that try to accommodate multiple platforms, with necessary tradeoffs being the result. I just want to use something on a Mac that is designed from the ground up to *be* for Mac and nothing else.
AIR.