It might be useful to look at Microsoft and their history with C#. C# was announced in 2000, the first really useful version C# 2.0 came out in 2005 and even today Microsoft apps written in pure C# are few and far in between (just UIs for visual studio, sql server etc.). So, I wouldn't be surprised if the Apple to transition to Swift doesn't happen for five years or more. There is absolutely no point for Microsoft or Apple to use C# or Swift when 95% of their legacy code is another language like C/C++/Objective-C. These guys have so much money they can pay people to hyper specialize in old technologies, I'm sure MS has some guys who work exclusively in COM/C++ or Apple with some guys who work exclusively in C89/BSD.

Having said that, pretty much everyone developing for the Microsoft ecosystem (native) uses C#. That has been true for almost a decade now. I suspect the same will happen with Swift and Apple and rather rapidly because the Apple ecosystem doesn't have enterprise customers holding it back. Most of people commenting here seem to already know Objective-C. However, consider someone new to the platform. Would you spend 1 year learning iOS programming using Obj-C or learn it via Swift? Apart from Swift being a nicer language to learn, the reality is almost all tutorials/books etc have shifted to Swift. Good luck to the poor sap learning iOS programming via iOS 6 tutorials and Obj-C and migrating to iOS 9.

I think the Swift 1.0 to 2.0 journey was quite painful, pretty surprised that Apple made so many breaking changes with poor tools support, but I feel 2.0 is where it feels just about solid to build all new apps. Sure there will be changes, I mean Obj-C had ARC and blocks twenty years later! but that's the nature of software nowadays.