Which was exactly my point. The tools for targeting javascript from other languages are non-existent at the moment, never mind mature enough that I would want to rely on them in production.

As an aside, am I the only person who reads things like this and is filled with a sense of foreboding:

The spec mentions cross site script inclusion issues that could arise from the consumption of a source map. To mitigate this it's recommended that you prepend the first line of your source map with ")]}" to deliberately invalidate JavaScript so a syntax error will be thrown.