Google is working on Nest Audio and Chromecast integration

Source: Google

One significant feature missing from the Nest Audio is its inability to serve as a speaker for TVs that use Chromecast. Its competitors—Apple and Amazon—allow their new smart speakers to work with their set-top boxes/media players to turn them into home theatre speakers. But now, Google confirms it is working on Nest Audio and Chromecast integration. The feature was already hinted at by the company in unused marketing material. 

Google hasn't revealed anything beyond that. And there are some unknowns regarding the feature. We don't know yet if you can use it with more than one Nest Audio at the same time. Or whether it'll support older Google speakers and older versions of Chromecast. We also don't know when it might arrive. The marketing material was supposed to be for the September 30th Launch Night In event, but it was pulled at the last minute, suggesting the feature wasn't and isn't ready yet.

Source: 9to5Google