With Apple having released Swift at WWDC 2014, I am seeing a rise in demand for Google to let Android developers use Dart. While I'd be glad to be proved wrong, I don't think that's gonna happen. Obvious reason: interoparability (or backward compatibility - whatever you choose to call it).
The ideal situation would be if the Dart VM itself were to form the runtime on Android but obviously that is out of the question.
Then, there is the question of skills. Google and Android benefit from the fact that the programming language used to make apps for the platform is among the most popular programming languages in the world. Why on earth would one want to throw away that advantage?
I think the better scenario is if Google brings Java8 to Android - particularly lambdas, default methods in interfaces and the improvements in the collections APIs.