Part if this is what your long term goals are. If you want a job vs want to make apps. In addition, game programming is different than business apps, etc...
Having a background in programming, you can jump right into what Ray offers or a language specific book. Big Nerd Ranch offers ObjC and iOS books that are great.
If you are looking at game dev, Unity is a popular path and might be a way to go depending on if you want a job or just to make apps.
In the end, programming is programming. Once you learn one language, learning another isn't such a big deal, it's mainly syntax.
The job market for Swift is still up in the air, we won't have a clear picture for a while, so knowing both is a good option.
Understand that there is MUCH more to app dev than just the language. The APIs and many other things are needed.