There was much excitement among audiophiles when the Sonos One was announced — there might finally be a voice-controlled speaker with half-decent audio quality that doesn't cost $400 (like the Google Home Max). It launched with Amazon Alexa (as did the Beam soundbar) and a promise of Google Assistant at some point this year, but that's sadly been pushed back to 2019.
It's already a whole year since the Sonos One was released, so it's a bit disappointing that they haven't sorted it out yet. There's no reason given for the delay, but the company says they're making good progress as they work with Google to make it happen.
In slightly more positive news, Sonos is recruiting users to beta test the integration, so it must be at an advanced stage. You can sign up to be considered as a tester here. The vague roadmap is to "start testing the experience in a few hundred homes at first, and a few thousand homes in the coming months." In the meantime, it might be worth trying a workaround instead.