I mean updating the runtimes to support the new editor features. Adding support for new runtimes would be a separate effort.
Unfortunately SpriteKit can't support some of the most compelling Spine features (meshes, FFD, skinning). Is there a reason you don't choose to use a different game toolkit? While I have experience with many game toolkits, I'm still completely biased and suggesting my own technology, but libgdx is very powerful, has great IDE support (Java in Eclipse is pretty amazing, Xcode doesn't come close), has hotswap on the desktop (change code while the app is running!), and you develop a single codebase then deploy to iOS, Android, HTML5, Blackberry, OS X, Windows, and Linux. libgdx has a 2D scene graph like SpriteKit, cocos2d, etc called scene2d. libgdx contains my UI toolkit (called scene2d.ui) that Spine uses (Spine is written with libgdx).