Idea of using Javascript as an intermediate for different programming languages is not new. I can say exact same thing about attempts to make browser runtimes closer to hardware. There was a big push toward JVM and Java in general at one point. Then Google did a splash with NaCl (which stand for Native Client). Developers needed a high performance secure environment to build efficient browser apps and have a path of porting existing apps from C/C++ realm to Javascript. asm.js supposedly is going to solve this issue by introducing a Javascript library and cross-complier from other high level languages into asm.js.
And this attempt is more serious than previous ones. For starters, it’s supported by Javascript godfather Brandon Eich.
Here’s his interview on this matter:
https://medium.com/javascript-scene/why-we-need-webassembly-an-interview-with-brendan-eich-7fb2a60b0723

From one side, this does not sound like a best solution for porting high performance apps like games (more exact, game engines), but since W3C will never come to agreement on lower level solutions, asm.js AKA Web Assembly may be the best compromise of the moment. It’s going to be based on many hacks and quirks. For instance, they virtually are going to disable GC. It did not take 20 years for web developers to understand that GC is a… garbage that they have to deal when it comes to speed optimization. There will be hacks around offline downloadable binaries or something like that. Otherwise, loading big games will be going to be a major pain. Anyway, it looks like major game engine developers are on board. Unity and Unreal already got prototypes and whole thing looks more promising than NaCl initiative.

Here’s another good article about Web Assembly:
http://ejohn.org/blog/asmjs-javascript-compile-target/