Of all the "Javascript.next" languages I hear on a regular basis, it seems to me Microsoft's Typescript is the one most likely to become successful, if only because every time I read an article about it, most of the comments are extremely positive about it and it looks like there are already some fairly large projects written in it.

In comparison, I don't see a bright future for Dart nor Livescript (although I secretly root for Dart because I have more confidence in Google to take this language somewhere interesting).