Google has released the beta of the Dart SDK which includes an editor with much improved code completion and analysis, so it might be regarded as another step toward an IDE of sorts.
The new Dart SDK includes an upgraded editor, written in Java, with a much better code analysis engine which reports warnings and errors at compile time. The new engine is 20% faster and it supplies the errors as you type.
There are a few additional new features - rename library refactoring, convert method to getter and vice versa, import library and create class and create part quick fixes. Probably the most important feature is that code completion is better. It will now recognize the nearest match based on a camel case typing of the significant letters - e.g. you type iE and it finds isEmpty.
The alternative is to use the Dart VM, which is now 33% faster and features brand new SIMD acceleration. It is also easier to deploy a Dart app using the pub deploy command, which builds a directory structure and copies resources to the server.
Dartium, the combination of Dart and Chromium is also now faster in WebGL.
The biggest news is probably that the SDK has now made it to beta. Who knows - one day perhaps Dart will graduate to a final release. Google, however, is well known for keeping projects in beta well past their testing date...