It is also not sure how long the service will work or be offered for free. Well, as far as I know, this service is used in devices that support Google home - the same as the Amazon Alexa integration on new Sonos speakers.
So there's hope that Google won't change the way it works all the time.
I have no idea how much work the development of this plugin will take - but the Wave-Net voices are great and I would be one of those who would donate for it.
But with all the enthusiasm for these great sounding voices - everything has to be sent to the Google servers and therefore doesn't remain private and you always need an internet connection.
Wouldn't that be a project for the winter?
Kalle