To add a few more useful links. Language spec[0][1] is available under a free license and they welcome input on it[2]. The 3 top starred bugs in their bugtracker are: enums, non-nullable types, and "await" support [3], though I don't expect non-nullable types to ever be added, but they like hearing what is important to programmers. If there is really a killer language feature that people want, starring it will increase it's chances of being considered.

[0] https://www.dartlang.org/docs/spec/latest/dart-language-spec...

[1] https://code.google.com/p/dart/source/browse/trunk/dart/docs...

[2] http://news.dartlang.org/2014/02/standardizing-dart-1st-ecma...

[3] https://code.google.com/p/dart/issues/list?can=2&q=&sort=-st...