Google's secret about DART

Short answer: No

Longer answer: The Dart VM would need to be adapted to battery powered devices as thoroughly as Dalvik. Android's runtime is not just for apps. Android's middleware layer runs mostly in the Dalvik VM. Implementers have multiple options for performance-critical code, including native code, relying on the Dalvik JIT compiler, and Renderscript.

Not impossible, but I don't see efforts in that direction. Then there are lesser details like adapting Dart to Android's security and IPC model, etc.

Until then, WAGs like this have the same credibility as predictions that Android will go JavaScript.