At this point Carbon is pretty dead. It has been deprecated since 2012 and nobody wants 32 bits apps anyway. So now with the transition to Swift and all the Obj-C types ****ery it seems inevitable that Apple will release a new SDK 100% in Swift. Another argument is that Apple could now have a cross platform SDK (macOS/iOS/watchOS/tvOS) which seems the most logical step. It would not surprise me if Apple announced this new SDK in WWDC18.