Definitely ready. I've had a Swift app out for 4 months and it's been quite successful[1], with no Swift-related issues.
I've just updated the app to Swift 2 and it's all working great.
The only issue has been related to the new Bitcode feature in iOS, which isn't Swift-specific. It's been very difficult getting third-party libraries with Bitcode support, but Bitcode is required for watchOS 2 apps.