I have released an app with Swift and libraries in Obj-C. Now I am developing an iOS game completely in Swift working correctly even in iOS 7. (Apple provides libraries to support Swift in 7, but in iOS 8 is native)

I think is more the contractor doesn't have the experience or don't feel confortable enough deploying a Swift App. There are some issues with XCode and Swift, but nothing too critical.

The language is ready, but most of the developers aren't.