Whilst Sonos CEO Patrick Spence earlier in the year at the SONOS IPO suggested that a December 31st deadline was when the Google Assistant Integration would be completed. However, according to a recent blog post on the Sonos website - It wont be available until next year. In the meantime you can still use your Amazon Alexa to tell your Sonos what to do.
Amazon meanwhile continue to bring out a slew of cheap priced smart(ish) speakers that must be eating into the Sonos product line.