Briefly. There are Kotlin areas in the codebases I work on, particularly in Android code. It's not something I've needed to use yet, but I've heard good things and I'm interested to get into it once we start using it more.
The best side benefit for our Java heavy org was that the migration risk is very low due to excellent JVM/Java integration.
As the project progressed we started adding more in Kotlin and it massively improved developer experience.