[akiselev]

Most news sources already load between 2 and 10 megabytes of Javascript, which is a significant fraction of, say, Python's runtime and many, many people browse those pages on mobile devices and connections without a problem. In Python's case, a large amount of the runtime size is taken up by all of the platform specific implementations of the standard library and they wouldn't work in the sandbox anyway.

Is there anything preventing Python.org from hosting the runtime environment on their CDN that everyone caches locally? Are there security issues from cross domain modules? Worst case, I don't think it would be hard to extend the LocalStorage API to cache modules between domains (perhaps with signed runtimes and a fallback).