So is Apple transferring its own app to Swift?
Maybe they eventually will be 100% Swift, but it's not practical to rewrite a whole project. There might be new classes for their Obj. C apps being written in Swift, since you can write apps in both at the same time.
Also bear in mind that those are not the only two languages used on Apple's platforms. For one there is Metal Shading Language, which is based on C++, and is used for GPU stuff. Then there is straight C, which you can write alongside your Obj. C code. And finally, C++ itself is still used for some parts of Audio Units (see the .mm files in
this example).
As well, Apple accepts apps written in Java (using
Google's j2objc), C# (using Xamarin), or JavaScript (using FaceBook's ReactNative [transpiled] or Telerik's NativeScript [custom runtime based on V8]). I'm sure there are others as well. People use these alternatives when they want to have a shared codebase across multiple platforms (e.g. iOS, web, and Android). You give up some of the advantages of fully native development in XCode, and you put yourself somewhat at the mercy of a third-party stack of dependencies, in exchange for writing less code.
Web developers may laugh at the idea of "being at the mercy of a third-party stack of dependencies," since that's what every web app is nowadays, but I mean, with a website, you control 100% of the stack all the way down to the version of linux the server runs on, and all you really have to worry about are browser-specific issues.
However, with iOS or Mac, you don't control whether users upgrade to the latest OS version the day it comes out. What if your third-party dependencies fail and don't have a new version yet? Just know the risks.
Sorry, that was a bit of a tangent.