Ecobee!
A better and faster integration would be to hook into Home Assistant. That will give you everything that they can see. Their entire project is integrations with Smart Products. The only requirement for hosts would to put a RaspberryPi($35 one time fee) in each home.
This is a HACS integration for Home Assistant that already can hook into a iCal feed
https://github.com/tykeal/homeassistant-rental-control
With OwnerRez support it can be done in a more official way.
