Nobody can build a nice app based on such an API. The official app tried - there were spinners on every part of the UI. Even simple things like 'give me a graph of network bandwidth' would have gaps in the graph where the single threaded service was bogged down with other requests.
Also read Build and I'm sure Tony is just sad at seeing the opportunity lost as Nest becomes a shell of itself.
Ecobee released their first smart thermostat 3 years prior to the first Nest Thermostat. (Not that that's a fault, I've been a happy ecobee user for years.)
It's a shame, Fadell was right to go into the thermostat market. Honeywell still has nothing that looks nice, and, according to the reviews, nothing that functions well. The stuff that comes with HVAC systems are generally expensive but cheap feeling and imho ugly.
In the EU all manufacturers have to support OpenTherm, an open standard, so you'd think this is a big homogeneous market to enter...
I've been reading "Build" by Tony Fadell. It's just painful to read what Nest could have been. The V3 is nice, but there are still rough edges, the app loads slowly for example. And it is absolutely ridiculous how much trouble it is to let it talk to Home Assistant.
At this point: Please Google just opensource the firmware or something, add a local api and be done with it. It feels like they just don't want to support the device. Such a shame, it's such a nice thermostat (hardware-wise an ethernet cable to the heatlink would have been nice, to optionally drop the dependency on wireless).