You're not concerned about fragmentation so long as there's a "lite" fallback. Got it. Let's see how this plays out. It may be that browser vendors with hot websites have to make the "lite" experience as good over time as their proprietary one, so they work fairly with the standards bodies.
Again, for this thread, per the leaked memo, that was not the plan with Dart. Coming to a standards body late will not work -- it may get a spec, but not Dart support in other browsers -- unless Googe has near-monopoly power.