At Google I/O 2019, it was announced that Google would be taking a Kotlin-first approach to Android from now on. This means that new APIs will be built with Kotlin in mind first. And, in fact, some APIs will only be available in Kotlin.
Additionally, new courses, documentation, and samples are being created with Kotlin and generally default to Kotlin over Java when examples exist for both.
IntelliJ and Android Studio both make it incredibly easy to integrate Kotlin with existing Android projects, or to start new projects that are 100% Kotlin. Additionally, Google continues to invest in Kotlin with improved tooling and the Core-KTX Jetpack library, which makes building Android applications with Kotlin even more enjoyable.
The Android architecture components are now built with a Kotlin-first approach and include support for Kotlin features such as coroutines. To an even greater degree, the pre-alpha Jetpack Compose library from Google is an entirely new UI toolkit built with, and for, Kotlin.
As these tools mature and new ones are developed, Android will continue to become more and more Kotlin-first.