Hi there - yes, it's partly about marketing message. When we did early validation, people were concerned about a 'custom language' - the reality is that the majority of the application is written in JS - the performance parts are in KL. KL itself is almost identical to JS, but right now you have to declare types. In the future we may switch to inferred types, at which point code will be indistinguishable from JS. Just don't use closures :)
Closures break the high-performance part of things. If we could have just used JavaScript, we would have done so - KL is as close to JavaScript as we can get, and still offer native, multi-threaded performance. If we introduce inferred types, then the only difference will be 'no closures'.
That makes sense, I'm sure it is hard to optimize closures and untyped code. However, if you remove those you no longer have JavaScript so it is incorrect to say that you have made Javascript fast, you've just created a different language and made that fast. Of course if it plays nicely with Javascript that's cool, but please say that!
