I don't think that it's the right approach only ever to allow JavaScript (just because every time anything else is mentioned, we inevitably go off on this tange

I don't think that it's the right approach only ever to allow JavaScript (just because every time anything else is mentioned, we inevitably go off on this tangent). There is no indication that browsers are going to standardize on a VM (let alone NaCl) any time soon. If someone just stopped bikeshedding and did Python in the browser, there's no reason a machine-level bytecode or whatever couldn't be implemented later.