> Any performance improvements seen by your users won't apply to those using any other browser.
But it will apply to those using Chrome (their performance benchmarks show consistent improvement, sometimes up to 2x) and it will be using a better language for all the other ones.
Dart -- without being in Chrome -- has the same userbase as CoffeeScript, ClojureScript, or any other language that also compiles to JavaScript.
There are some real potential wins with being in Chrome, many of which are political, but there are no technical reasons for not being in Chrome to block Dart's adoption.
Except Dart isn't trying to be another "compiles to javascript" language like CS, Dart is trying to completely replace js which is why it's so much more difficult to implement. They have to build an entire VM to rival V8.
But it will apply to those using Chrome (their performance benchmarks show consistent improvement, sometimes up to 2x) and it will be using a better language for all the other ones.