This joins generators[1][2][3] (Andy Wingo) and arrow functions[4][5] (Adrian Perez de Castro, Andy Wingo) as examples of the community (read: not employees of Mozilla, Google, Apple, Microsoft) directly working on the engines to ship these features much sooner than they otherwise would be. (Surely they'd land eventually, but acceleration and cross-engine coordination greatly improves time-to-dev-market.)
FYI Chrome will ship with async/await support[0] in the next stable version (55, so it's already on Chrome Canary).
[0]https://bugs.chromium.org/p/v8/issues/detail?id=4483