That's a great attitude for the browser--and I completely agree that decentralization is important for the browser--but does your opinion here extend to server-side JS as well?
There is that saying, "The Medium Is The Message." The more restrictive the medium, the more restrictive, the more pre-defined, the message is by default. The less restrictive the medium, the less well defined is the default message.
If you want an analogy, think of a knife. It can be used to cut things very well, but also serves as a really bad screwdriver, bottle opener, toothpick, tent peg, etc. Better to have a tool for each of these tasks than cut your thumb open mis-using your knife.
We maybe need one general-purpose language for trying new stuff out (and I'd argue that that language is actually LISP). The rest need to be single-purpose, designed to do a single job.
Javascript is designed to run in browsers, and recently to run on a server (mostly as a web server). Trying to write real-time systems (for example) in javascript is a bad idea; you can do it, but you will cut your thumb open and there are much better languages available to do it in.
I think the core point I'm trying to make is that programming languages are engineer's tools rather than artistic media. We use the tools to build the thing we want. Tell an engineer that the hammer is the thing being built and they'll tell you you're an idiot.
Then it will be more like Java Applets or Flash applications, I think some restrictions have lead to better index ability(hyperlinks, search engines) , accessibility in web.
A better medium doesn't necessarily mean untamed or freer medium. If restrictions can create a medium which has better accessibility, then maybe they are not so bad.