So... I'm still thrashing on thermostats, but today I feel optimistic about the Radio Thermostat CT50 - so much so that I ordered two of them off Amazon. The company publishes an API that is locally callable over http, and I don't believe it's necessary to have them connect to the vendor (although it's possible). There is even a perl module in CPAN for the API. I feel sort of stupid for not seeing these earlier. I will post an update once I have them installed. I plan to create a dedicated WIFI network that does not have internet access and put them on that.
I also looked and (and ordered and received) a