This looks cool! It's not as simple as just "switching it on" though. Past experience suggests Optus won't launch this feature as there's not a huge market for it at the moment. Look at visual voicemail as an example, an amazing service that enriches a users mobile experience but it's not well known enough to push Optus to provide it
I can't say that I've heard any talk around voice activated calling for the Google Nest.
It's not something that's currently on our radar.