Cool news in SmartThings/Google Home/webCore…
@ghesp has a pre-release version of a capability to send voice notifications to Google Home, and avoids the pitfalls of TTS…as Greg notes:
“Note that this is NOT a TTS service, so it does not rely on the casting audio feature. This means that even if music is playing, the music will pause, the message will play, and then the music will resume.”
It relies on a node.js server (I’m using a $49 Raspberry Pi) to provide the Google Assistant relay, and can send custom text entered in a piston, and can also use a number preconfigured Google Home broadcasts.
It’s still in development, and any of the slightly more techie types here who have or want to set up a box w/node.js to run the relay can start playing with it and have announcements on their GH devices and provide feedback on issues.
It is pretty awesome. 
Quick and dirty piston example:
Using custom text string:
Using one of the pre-configured broadcasts: (Available: wakeup, breakfast, lunch, dinner, timetoleave, arrivedhome, ontheway, movietime, tvtime, bedtime)
Parameter options:
