FWIW, Nest products were never very open. I had one pre-Google acquisition, and there was never a way to talk to it that wasn't via Nest's own servers, even though it's on my network.
Of course, the likely thing is that Google will not go out of their way to make it possible to make Nest plugins for Alexa, Cortana, etc.
Of course, the likely thing is that Google will not go out of their way to make it possible to make Nest plugins for Alexa, Cortana, etc.