Last year on november, Google said that they will let everyone know if using HTTP/2 is safe for them by the end of the last year. Unfortunately that never really came out but they do told us that there is no SEO advantage of HTTP/2 later on this year.
Yesterday, Google on Twitter gave everyone official permission to go HTTP/2.
You can see the tweet below:
Setting up HTTP/2? Go for it! Googlebot won't hold you back.https://t.co/3bf5Kd2Eo8
— Google Webmasters (@googlewmc) December 19, 2016