So, one of the complexer part of Java isn't completely finished, and they want to postpone the release instead of releasing something buggy. I'm fine with that. Everybody survived with Java6 for half a decade as well. And three years with Java7.
Most likely it will never see 100% support for Java 8, or anything else that comes afterwards.
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. :)