It is hard to predict the future, but I do think this is a very positive move for Dart that will drive adoption.
Dart frameworks were always playing second fiddle to the needs of Javascript developers - resulting in compromises.
A Dart first framework (with some awesome Material widgets thrown in) will offer a compelling developer experience.
Combine that with Dart on Mobile (flutter.io), Dart on IoT (dartino.io) and Dart on the server, and you have a very nice story.