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.
I agree that having a robust dart-first framework (and widget library) is a necessary condition for making dart popular. Here's hoping it is also sufficient. I feel like Dart lost its biggest edge when google moved away from the dart runtime. If everything is just compiled down to js anyway, dart can't do much more than put syntactic sugar over what's already there, instead of providing a real new language experience.
Then again, clojure, scala, and java are really different experiences. Maybe google's backing keeps the language running long enough to gain real traction.
Why should I learn one or the other?
If the ideas and concepts behind dart are so good why isn't golang taking input from it?
If golang is so good why does dart even exist?
Of course that means you can't share code between client and server, but not everyone needs that.
"If you're a TypeScript or JavaScript developer, you'll also benefit from cleaner JavaScript APIs and performance gains as we simplify the TypeScript codebase to remove the need for compilation to Dart."
Maybe this split was prompted by the imminent release of Typescript 2.0?
I honestly don't see how a low-penetration language is going to benefit much here - are we going to see a resurgence of interest in dartlang just because now there's a more native-feeling angular library for it? I've been wrong in the past, I guess.