I'm really curious about Dart's future. I also see it as an "enterprise" alternative for JavaScript, but I don't know if that is enough to make it fly. I've actually started a discussion about it right here on echo a few weeks back, and interestingly, no one mentioned the risk of seeing Google just killing the project if it doesn't get the "expected" adoption. In my honest opinion, that risk is actually pretty high.
By worthless, I was alluding to the fact that all the performance related benefits are still hindered by browser incompatibilities and lack of support by other browser vendors. As an ecosystem, I think it is a pretty interesting piece of technology. I just have my doubts that it actually solves any "huge" problem. But I can imagine a good use-case, the enterprise. I believe something like Dart is more appealing to hermits who are still working with Java and .Net Stacks for the web (intranets and stuff like that). However, I just don't see it succeed with open-source, modular and startup-type tech. Again, I can be completely wrong about it, but if I'm allowed to use something like Node.js as a benchmark, there seems to be a huge difference in terms of adoption and growth speed between both, obviously in Node's favor. Anyway, you make some good points and I hope to hear from more people about it.