I'm very keen on the idea of cross platform Swift just now.
Swift is a great language which manages to be easy to use while being powerful, two traits that most languages just can't claim. As such, I am already seeing a surge in the interest of this language, and once the Foundation settles down and writing Swift for other platforms (especially Android) becomes easier, I can fully imagine that it will become an effective cross platform tool that will basically make the likes of Xamarin redundant.
In the mean time there is a way to go, but I haven't seen such enthusiasm for this since Java.
Check out the following links:
Altconf: Cross Platform Swift - https://realm.io/news/altconf-boris-bugling-cross-platform-swift/
Swift in the Google Play Store - https://medium.com/@ephemer/why-we-put-an-app-in-the-android-play-store-using-swift-96ac87c88dfc#.9tgt30q7h
There's already a couple of web server implementations. I have already had great success with PerfectServer.org and the above Altconf video talks about Frank. High performance micro-services written in Swift? Yes please.
The language has a great future, but it makes me wonder about the value of another really interesting project: J2Objc, a transpiler that takes Java code and spits out Objective-C. Google already used this to achieve 60% re-use across iOS, Android and GWT. But are its days numbered?
That's enough gush for now, I'll keep on eye on the progress of Swift as a cross-platform language and report back as news comes in or when I get around to doing experiments.