Getting back to the original question…
I looked at the Venstar T5900… it looks like a possibility, but availability is extremely low and the cost is very high. In my configuration, I have three zones, so the cost is an issue. Programmatic control is more important than a fancy wall unit.
I really agree with @oskrypuch
I used the Venstar T1700 and T1800 for a very long time, but when my PLM started to have issues and the future of Insteon undefined, I switched everything to z-wave and a few node servers using WiFi. From a responsiveness point of view, the 1700 and 1800 were instantaneous. Newer thermostat designs have some more heating system parameter control options and a smaller temperature resolution, but these older models worked fine. I still have the units, so if Insteon ever releases a new PLM, I might consider putting them back to work.
The basic question is… are there responsive non-Insteon thermostats that can be fully controlled with IoP through local control (WiFi, Z-wave, Zigbee or the up and coming Matter)? The thermostat needs to acknowledge temperature changes as they occur, preferably in 0.1 F resolution, but 0.25 F will work… and the change has to be available to the IoP with a very short delay.
Based on my experience with Ecobee… I love the options/settings that can be controlled programmatically, but with no local control, the changes can take up to 4 minutes to register from the IoP - to the node server - to the Internet - to the Ecobee and then back to the IoP. So, I tend to feel that hardware requiring a node server is not going to be ideal for HVAC control.
