js2-mode supports ES6 fairly accurately. But of course, that's not enough, people keep asking for new things: JavaScript mixed with HTML, Facebook Flow support, JSX, new ES7 (still unstable) syntax extensions, and so on.
It would be easier with a more stable language. I.e. not JavaScript, which is still going through growing pains.
Even so, "25 Open, 204 Closed" seems pretty good to me.
fundamental-mode hasn't failed me even once, is what I mean. :) I'm not criticizing js2-mode, it's just that I have personally given up hope for accurate language modes in general, and realized that they are a lot of effort and IMO relatively little use.
It would be easier with a more stable language. I.e. not JavaScript, which is still going through growing pains.
Even so, "25 Open, 204 Closed" seems pretty good to me.