Also, you don't have to use Eclipse or Android Studio at all if you don't want to. You can use whatever text editor and whatever build system floats your boat (ant and gradle are common).
The only time I use either of the Android IDEs (Android Studio, because Eclipse is horrible) is when I need to do on-device visual debugging; otherwise I just do command-line builds and deploy using adb.
Probably the best move for Google would be to write a super fast WebView implementation. This will let the huge mass of web developers to use JavaScript at a speed comparable to Java.
Open source or not, Swift will never be appealing for the world outside Apple's garden if it will be as intertwined with Cocoa as Objective-C currently is. It will be nice however to see how well Swift could be ported to Android.
This is probably the biggest announcement from a developer perspective. Swift looks like a language in which you can code as fast as you code in languages like Ruby or Python, while having the speed and performance of a language like Objective-C.