Thats smart 
Except, in my plans…
… is a bit tricky, cause I will not be using web audio. I will be using chromecast´s devices as “speak to”, as well as “listen to” TTS audio. And even more, I plan on making somekind of presence detection, and only send TTS audio to that/these rooms where presence is detected. I know, this will require rather advance rules. But at least thats an idea. 
I know how to cast TTS audio to chromecast devices. I already do that with the one Google Home Mini I´ve got. My concern is, how to cast TTS audio to an Android tablet. I dont even know if thats possible, unless I´ll be using the web audio. I guess this is a question to be searched for…