While Kotlin itself is a nice modern swift-like language, it'll never get the same type of adoption unless Google makes it a priority.

I'm a lead Android developer and I've inherited a Kotlin codebase mixed with Java, and here's why I refuse to create any new classes in Kotlin:

1). Compile-time is slow. I know there are plenty of work-arounds but I don't want to modify the build-properties to the point where it's hard to replicate when onboarding new engineers. The closer to the default-project settings, the better and the less resistance. Android dev itself is a very fragile framework to begin with.

2). Abuse with nullable types. I've been a lead iOS engineer too and this is what I have observed as well with Swift. I can't even count the amount of Crashlytic reports that have been caused by a model not binding properly.

3). It really doesn't save that much time at the end of the day. A language is a language is a language.

4). Community/docs does not have as much reach as Java in terms of docs.

This speaks more to the previous developer than the language itself, but this has been the most unstable code-base I've ever worked with.

I specifically avoid web-development for the bandwagoning hype when the shiniest new piece of tech comes out. While I think it's great that Jetbrains is trying to make a competitive language to Java, I think there are too many forces working against them.

Java's old, boring and predictable, but that makes it a great language to a build a stable app with.