The plus side is that Google can develop Dart alongside the framework. This allows some nice things like excellent hot loading support, fast AOT compilation for

The plus side is that Google can develop Dart alongside the framework. This allows some nice things like excellent hot loading support, fast AOT compilation for release builds, a GC tuned for UI work, etc that would be harder or even impossible in a general purpose language with different goals. It's also a pretty easy language to learn if you're already familiar with any other modern mainstream language.