I’m confused: I thought you were recording guests’ comings and goings. Why not place the camera externally then, to view the entrance door area (assuming an entrance from outdoors)?

Contract or not, indoor cameras are begging for a lawsuit, if not criminal charges. Remember that invited guests didn’t sign the contract, so they didn’t consent to be spied upon in an area with an expectation of privacy.

And if you ended up losing a lot of money to a judgement and legal fees, I wouldn’t have an iota of sympathy for you.

As far as ipv6 thermostats, someone will make them. If only for commercial buildings where the designers don’t want long-term vendor lock-in.