Source maps in Firefox and Chrome will be one of the most important pieces of software infrastructure since Javascript itself. It will be the realization of Stallman's "one script to unite them all" vision for GNU GUILE from the "Tcl wars." A pity that it isn't Lisp, but there is enough goodness in Javascript (and Coffeescript) to make me very optimistic.
Source maps are relatively easy: There's a public standard, a couple of browser makers have agreed to it, and it doesn't need universal acceptance since it's only for development. Basically, it doesn't require a lot of coordination.
A universal bytecode is almost the exact opposite — easy to describe in the abstract, but a coordination nightmare. I've never heard an actionable plan for making it happen. Just getting the community to agree on a standard bytecode would be a Herculean task†, and then you have to get Apple, Google, Mozilla and Microsoft to all say, "Yes, I'm willing to chain my VM to this bytecode at significant engineering expense."
Basically, feel free to work on this if you want, but you can't expect everybody else to hold their breath until it happens.
† You might think that "Herculean task" is an exaggeration, but just look at how much discussion and compromise was needed to get agreement on stabby function syntax for Harmony. And still people kvetched even once there was "agreement"!
At any rate, any bytecode the JavaScript VM people agreed to would almost certainly correspond very closely to JavaScript, so it's not clear that a standard bytecode would make alternative languages much faster. On top of that, the optimizers in current JavaScript implementations are highly tuned for JavaScript, so a bytecode-compiled program running on V8 might actually be slower than the JavaScript we have today.
Basically, without an implementation, this all sounds like pie-in-the-sky talk to me.
You have what you want. You don't have to right in JavaScript any more. There are dozens of alternatives, and there are only going to be more. Source maps means you'll never even have to look at JavaScript. Please be happy!
Source-to-source-translation _always_ sucked and that's known for a few decades already.
The bytecode that browsers compile JavaScript to are incompatible with each other. They would either have to pick one (wouldn't happen) or design one together (wouldn't happen).
A designed by committee bytecode would also effectively eliminate browser vendors' ability to compete on speed.
> Source-to-source-translation _always_ sucked and that's known for a few decades already.
In what way? From what I read Gambit Scheme compiles to C that is as fast as hand-crafted C. I would assume that CoffeeScript is no slower than regular old JavaScript. So if not speed, how are these things sucking?
>But why is this REALLY COOL? Because I can potentially debug any language in the browser as long as it has a source map.