Maybe eventually we will have 'sufficiently smart transpilers' and interactive debuggers for languages that target javascript and don't expose the 'JSVM' but that is not the case at the moment. Mozilla said "And if your problem is with JavaScript as a language, you can already use a myriad of languages that reliably compile to it", i.e. if you don't like javascript you don't need to use javascript. This is what I was responding to, because I don't see it being true in the near future (next several years at least).
Right now source mapping is only working between uncompressed/combined JavaScript to compressed/uncombined JavaScript
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.
