With the Java interop such a high priority for the Kotlin team over at JetBrains, Kotlin is sneaking its way into all kinds of Java environments -- from LOB apps to APIs, Java Web Services, etc.

Java might be a little annoying to wield, but the JVM is actually quite nice.

Whomever at JetBrains put a premium on Java interop should get a medal, because it's a VERY low friction move to go from Java development to Kotlin. You can port your project one file at a time and the tooling is excellent.