I have many devices which report temperature, but only my thermostat is included in the “Climate” devices. There doesn’t seem to be a way to add devices to Climate, like you can with lights or doors. Am I missing something ?
No, the Climate summary shows thermostats only. Maybe a separate summary element… 
Then when you click on the info “I” it shouldn’t say “Devices with Temperature Measurement and Thermostat capabilities and temperature reading.” … That is not accurate.
I agree the this might seem misleading, but the key word is AND. Is not an OR to inply that it can be any. So theoretically the note is accurate. Nonetheless, we can make it more clear.
Isn’t temperature measurement implied as a basic function of a thermostat? Hard to regulate the temperature of an indoor space without measuring it.
I was expecting the additional remote Honeywell sensors to be listed. Possibly even other temperature sensors. Showing the setpoint on the home display makes sense, but clicking on the “Climate” should bring up all the temperature sensors that I have selected.
You have a point, but Climate in the HVAC context refers to the active regulation of the indoor climate, which describes the thermostat function. Temperature from the thermostat is included, because it is the specific temperature sensor that feeds the regulating device. In this context, though, your Honeywell temp sensors are directly feeding into the regulating device, so by definition they should be included, but by practicality they are left out because they are not a temperature attribute state on a thermostat device, defined by the thermostat capability.
If you have the code for your temp sensor drivers, maybe you can just add:
capability "Thermostat"
to the top of your driver definition for those sensors.
I am using the community Honeywell driver. I definitely could add that capability line. I wonder WHAT the impact of that would be, since the remote sensors are just that – sensors only. No capability to change anything.
I guess I am of the opinion that “Climate” should include all reporting, rather than just capability to change.
I don't think you would even notice it. The driver will have defined attributes for the thermostat capability, but nothing will set them, so you should never see them. It might put some thermostat commands on the command tab, but most commands need to be defined in the driver to actually do anything.
The temperature sensor devices would then show up in apps under thermostat devices for device selection in apps.