I'd be willing to bet against it. There's so much cruft that has to be kept in for compatibility reasons that I really doubt it. Also, the Mac offers much more functionality than an iPad, you'd need to expand UIKit a lot to run on Mac hardware. Maybe they deprecate AppKit and introduce UIKit alongside, like with Carbon, but I doubt they have the manpower for that right now. I guess they'd rather concentrate on making UIKit better on ARM than porting it somewhere else