If you can get away with using it Kotlin fixes almost everything I dislike about Java and works for Android development today.
Still checking in how Kotlin support evolves, my experience using languages like Turbo Pascal, Delphi and Oberon made me weary of using using languages that aren't directly supported by platform owners for production code.
It may not be supported by Google but it was created by Jetbrains, the developer of Ideaide which is what Android Studio is based on, so it's support is top notch.
The best part of Kotlin is there is near zero cost to using it. You can learn it in a day and is fully interoperable with Java. :)