Thanks for v1.8. I checked the Quick Changes device and it seems to be working for me within scenes now. Still can't use the thermostat device in scenes, but I can do what I need to do with the Quick Changes device.
I probably shouldn't push my luck, but I have a feature request. The eccobee3 supports different Hold modes: hold indefinitely, hold for x hours, hold until next scheduled activity. The plugin currently does indefinite holds. It'd be nice if the plugin supported some of the other hold modes at some point in the future.