Either by recognising certain URLs such as https://ajax.googleapis.com/ajax/libs/jquery/1.6.1/jquery.min.js, JSC could load a bytecode representation of the library instead of loading the script, circumventing all the HTTP requests and JavaScript processing that would normally occur. These would ship with JSC. And when encountering newer libraries (or perhaps any JS file), instead of caching the JavaScript file, the bytecode generated from it could be cached instead / as well.
Storing external libraries which are not part of the ECMAScript does not really make sense to me.
Integrating JavaScript libraries does reduce need to adhere to standards from ECMAScript or W3C or WHATWG. I am going to mark this as "RESOLVED WONTFIX". Thanks!