EDIT : just to be clear, I won't advice any sized team to go with staged features. It works for me because I do a lot a small sized project working alone on them and I'm ok refactoring their codebase if a feature implementation change.
I didn't know it was still in progress... really hope async/await makes it in. I'm betting on that pattern to make JavaScript much more pleasant to write!
It'll probably make it into ES2017, given that Edge, Chrome and maybe FF will have it in their browsers by the end of next year, official spec or not. It's a popular feature, and with Promises and generators in place, easy enough to support.
It really does cleanup a lot of code, but getting people to understand that an Async function returns a promise isn't always the easiest thing to convey until after it's been used. I resisted Promises for a while, once it became a part of ES6, and with async/await in Babel, I started using it... the cleaner code is worth the minor bit of overhead.
It certainly takes its time :) Well, Bublé sound cool for projects where feature stability over time is critical (like huge codebases), but I will still prefer to go with babel to select which stage I want.
EDIT : just to be clear, I won't advice any sized team to go with staged features. It works for me because I do a lot a small sized project working alone on them and I'm ok refactoring their codebase if a feature implementation change.