The chrome guys who started the sky experiment, now flutter, used JavaScript for the first few iterations. I think they went with Dart because they were able to get the Dart GC customised for flutter. The big feature that the Flutter team got from Dart, that they didn't know they wanted, was stateful hot reload.

Seems being able to build UIs with hot reload feature is a winner.

Norbert's experiment, looking at building an editor in flutter, looks very cool. As he says it a lot of work building everything from scratch, but starting with a widget editor is a cool idea.

The concept, in flutter, of every thing being a widget, even the app itself, is very powerful.

I agree, time will tell, with people like Norbert, who are outside of google, I'm interested to see what they and Google do with flutter this year.