Since Dart can compile to Javascript but it also has optional static types like TypeScript wouldn't it be possible to have a Dart to TypeScript compiler? I guess it would make the work easier for the Dart folks and allow compiled Dart libraries to be integrated with other TypeScript libraries.

Since Dart types are not required to make sense, only a subset of Dart programs probably make sense in TypeScript. It seems like an interesting tool that could be useful for both Microsoft, Google and the web community at large.