I didn't consider Kotlin in my projects because I believe Java will ease the transition process to other projects where Kotlin is not adopted. Even though that hasn't proven itself useful and I haven't changed my mind, I am thinking about transitioning the TrebleShot project to Kotlin for reasons I will talk about in this post.
Android has always lacked some features of Java and been slow to adopt newer versions. Java 8 support has landed only recently and some features are still unsupported (e.g. Modules). This isn't an issue when you don't need libraries targeting JavaSE, but it is guessing game when you do.
Kotlin fixes this fragmentation caused by the Android platform. It adds an extra layer that ensures your code works on different versions of Java. This is a good reason for a switch if you want to focus on the problem rather than the code or the platform.
Google has also made clear that Kotlin is a first-class citizen in Android development, making it more appealing. This also suggests that newer libraries will see a special Kotlin treatment.
This interests me enough that I am willing to move away from Java for my existing Android projects. TrebleShot is one of them and has a vast codebase that will take time and it will take some more if the work is not organized and done chaotically. I have a long list and it is growing at a slower pace than the universe expands.