That's what I was getting at - that JavaScript is popular because of the position that it is in (not because of the ECMAScript specification). JavaScript could have been a number of languages, the fact that it happened to be JavaScript, is more a result of a externalities than the language itself.
JavaScript was originally developed on an incredibly short development cycle, so I would be very surprised if we couldn't create a better language for the browser after 15 years of experience.
As far as JS on the server - I don't really see the advantage (other than it's a language that people already know). Having written several Node apps, using a single language didn't strike me as a "killer feature" (especially since their usage is fairly distinct - manipulating the DOM vs manipulating data stores and what have you). Different tools for different problems. I don't see JS as being superior for solving server-side problems.