I've found success with Kotlin stems from the great standard library, tooling, null safety, ergonomics, etc. Definitely not advantages limited to a particular domain. FWIW we (Netflix) have several teams doing service development with Kotlin in Spring Boot, some green field, some established projects. In terms of my team - Spinnaker, our continuous deployment platform has started adopting it - that work drives a lot of
https://strikt.io/ development to support those efforts. Much of our Java build tooling (Nebula) has moved Kotlin from Groovy for performance and reliability sensitive use cases. Astrid our dependency insight and change tool is all Kotlin was completely converted from Groovy during pre-beta of Kotlin