Well what you have created here works. And works better than all the other solutions that send Chromecasts TTS audio. You have created a way for 1 to use true announcements and 2 to utilize the built in grouping function and 3 volume control (especially through webcore)! First thing I implemented was to change the volume on my Google Home’s based on time of day and location of that particular GH. I have one upstairs near my children’s bedroom that now get’s turned completely down at night so there is no fear of an announcement or a random wakeup making noise.
And while something like this is interesting:
What you have here is much more useful/powerful as far as groupings, individual GH assignment and webcore integration. Hell I bought a PI3 just for this project.