It's true that Kotlin wasn't a breakout success 5 years ago. However, I would argue Kotlin's design decisions made it destined for its current success, whereas

It's true that Kotlin wasn't a breakout success 5 years ago. However, I would argue Kotlin's design decisions made it destined for its current success, whereas Dart has not. The most obvious of this was same-build compatibility with Java. Mixing Kotlin and Java made it super easy to switch, and made using it a no-brainer vs other solutions. Android Studio also has a button that auto-converts Java to Kotlin, so in many cases a wholesale rewrite isn't even necessary. At this point, Kotlin has also become a goto for backend Java for stream processing and other open-source JVM projects. It's rapidly replacing things like Scala for Flink, as an example. Maybe Dart survives by the sheer force of will of Flutter, but I don't think there's a chance it catches Kotlin.