As the article described, JS engines are not implementing features in "spec order". I expect async/await to get wide support fairly soon. (Though my opinion doesn't count for much. I work on SpiderMonkey, but I'm not the one who'd be finishing up our implementation, and I don't know where JSC and Chakra are on it.)

It's a bit of a funky one because it expands the scope of ES into what has traditionally been rendering engine territory (as in, an event loop). But I haven't seen resistance to it.