I think sooner or later a more agnostic VM in the browser will came. HTML was for hypertext, now (almost) it is for general UIs.
The problem is how to make a standard if organizations like Mozilla are not part of that? I think it is not so difficult: don't have a VM? emulate it with asm.js. Do you have a VM? run your application at full speed in more advanced browsers. When Google Chrome came with a faster Javascript engine, others needed to catch up.