Apple has some ARM source code on opensource.apple.com. I think this means OS X 11.x.x runs on Intel & ARM processors, like Windows 8.
No, that's iOS.
Apple need a big developer release if they want Mac app creativity to increase. AppKit has a lot of extremely complex and awkward to use controls. Apple need a simpler, more refined set of controls closer to UIKit.
Making a great mac app is far more involved than making a great iOS app, especially for beginners. The Mac should modernise its API.