Think of JavaScript as the JVM, CLR or ABC of the Web runtime. Now imagine someone trying to add a sperate bytecode/intermediate language to those runtimes. There are security issues and architecture issues to consider.
The language monoculture problem exists just as much on other runtimes as it's does on the Web. It's just nobody is expected to write in JVM or CLR.
That's why projects like asm.js and Emscripten are important. These projects show vendors what things are needed to make JavaScript into a better compile target so that someday writing in other language for the Web is as natural as it is on JVM and CLR.
The language monoculture problem exists just as much on other runtimes as it's does on the Web. It's just nobody is expected to write in JVM or CLR.
That's why projects like asm.js and Emscripten are important. These projects show vendors what things are needed to make JavaScript into a better compile target so that someday writing in other language for the Web is as natural as it is on JVM and CLR.