Turns out that people who already are happy with an alternative solution are less likely to switch than people who are already unhappy with the alternative because they are not yet used to it/invested and judge it with fresh eyes (like people from other camps like Python, Ruby, Scala, C#, Haskell, Clojure, …).
I personally find it sad that there is such an aggressive backlash against Dart from people who did not really take a close look at Dart or dislike Google for some reason (see Paul Graham's essay on how to disagree http://www.paulgraham.com/disagree.html).
If you look at decent JavaScript coders who are fluent with many programming languages they tend to see Dart in a different light, take it for what it is and judge it on its own merit.
Maybe focusing on getting the JavaScript community excited was a bit too optimistic. I don't know, you gotta try right?
That said, Dart seems to have an easier time with people who come from languages other than JavaScript or with people who only briefly learned JavaScript to do some stuff and wonder why they have to avoid 90% of the language and every library out there uses a slightly different not completely compatible set of conventions to emulate classes, promises, packages …