Dart may not be a standard yet, but both the Dart language and the Webkit source code are open.

Comparing this to Microsoft and ActiveX is an unfair comparison, imho.

2 things can happen: either Dart falls flat and this has no implications to anyone, or Dart becomes a major success and nothing is stopping IE, FF or Opera to writing their own implementation based on the open specification and code.

I fail to see the problem.