Yes, I think so too. The question about the need for an isolate has been asked by a Google's own Dart evangelist, so it's on their minds at least. Notice there wasn't much of a response. It's not a hot issue, but I think it will be.

https://groups.google.com/a/dartlang.org/forum/#!topic/compi...

TypeScript is good that you can transition gradually. I've been using it for the past week and it almost feels like working with Dart with the advantage that's it's just JavaScript. TypeScript interfaces to hundreds of JavaScript libs and jQuery plugins have already been written.

I imagine I'll settle on Dart for some things and TypeScript for others and maybe eventually get them working together.