There is a fundamental problem with moving the definition of web applications to being JavaScript/Python/Java-centered. It offends one of Berners-Lee's principles of web architecture: the ‘principle of least power’ http://www.w3.org/DesignIssues/Principles.html#PLP. That allows the substance of the web to be accessed, analysed, processed by other unforeseen applications. But encoding everything in/around a full programming language is very opposite to that: obscure and un-manipulable.
There is certainly a place for JavaScript-like power – very specialised, low-level tasks, perhaps like the core of Google maps interface. But there needs to be a general framework; an explicit standardisation of app/interaction structure. And this would be in a simple, declarative form, maybe something like SMIL and XUL. Actually, W3C has begun to develop something that might form the basis: CDF http://www.w3.org/2004/CDF/, but probably few have heard of it even, and it lacks important stuff . . .
The application structure could then be moved as much as possible into that, or JSON, XML, or similar. So the browser has a fairly simple and very general app-engine, and everything specific is in a simple, open format. In a sense: turn as much as possible into ‘content’, including interaction and app intelligence. Then, like other ‘content’ like movies or music, it is dumb, but infinitely accessible and manipulable.