To me, asm.js looks like a bad kludge -- and a great road ahead, just extend it a little bit over the next decade with the stuff compiler writers will clamor for.
Am I missing something?
Compiling other languages to JavaScript is a tolerable transition mechanism while browsers that don't support something better are still popular, but trying to improve the ability of browsers to interpret compiled-to-JavaScript code from other languages is farcical -- if you're going to update the browser then update it to support something better than JavaScript, not to improve the performance of the horrible legacy transition kludge.
But I'm cynical about the possibility to get a new bytecode standard out, without e.g. MS sabotag... extending it. Half the value of asm.js should be that if there is a working system already in place, the motivations for such shenanigans lessens.
The way to handle Microsoft in a situation like this is to ignore them. Support the same IR on Firefox, Chrome and Safari and then Microsoft can play along or go home. At that point the worst they could do is implement an extended version that allows sites made for all browsers to work with IE but then encourage developers to make sites using Windows-specific features that won't work on other platforms. That's effectively what they tried with Silverlight and you see how far that got them.