Dart is being positioned as a cross compiling, Android and iOS (but not web) development language with the Flutter platform. It very much seems like a replacement for Kotlin's usage on Android, but only if you are also switching to this UI framework.
It has a very long road to travel regarding OS APIs and the Android team evaded the question at Google IO about what was their opinion regarding Flutter.
Additionally, according to the Chrome team, also at IO, the way to do iOS and Android development is via PWAs, not Flutter.
https://medium.com/dartlang/announcing-dart-2-80ba01f43b6