It's one thing to have hot reload and another to have it also preserve the whole app state like Dart/Flutter does.
What Java brought, we already had in the form of Eiffel, Oberon, Modula-3, Smalltalk, Component Pascal, Dylan, they just suffered from not having Sun's budget offering a compiler and training materials for free.
Now they are trying to bolt into Java, features that some of those languages already had, but Java 1.0 ditched them like value types, AOT compilation to native code and proper generics.
I am betting that Dart will never have any relevant market share besides being the Flutter's language.
Android team is betting on Kotlin/Native and Jetpack Composer, so lets see who will win the internal politics.