I'm not sure, but I know the Gradle people worked with Jetbrains to integrate it into Gradle, so you can use it instead of Groovy. SpringBoot initializer will allow you to choose Kotlin as a language (along with Java and Groovy). Corda (an open source distributed ledger was built with it) - not sure how many are using Corda since it's so new. Quasar (an JVM actor library) supports it. Here's an article about KeepSafe converting their Android app: https://medium.com/keepsafe-engineering/lessons-from-convert.... There are several companies listed on the Kotlin website as well.

edit: The list of companies from the Kotlin website: https://github.com/JetBrains/kotlin-web-site/blob/master/dat...

I guess my point is you can find people using it. I just wonder why anyone who is currently using Java doesn't at least consider it and try it out -- it's much more concise and nicer to develop in. But then again, I guess a much larger percentage of Java developers don't ever learn anything new and probably have never even heard of the name.