All true. But I think the potential benefits are real, and I don't necessarily think it's a bad thing if the JS VM was specialized for JS. Standardizing the byte-codes could allow a looser coupling between browsers and JS. It could also allow for people to play with JS optimizations and augmentations without having to touch the VM internals itself.

All of this makes me think that if I was a VM researcher, I'd seriously consider going in this direction. And not being a VM researcher makes me think maybe I should be one.