Add option for multiple neck sizes under one diffuser tag in the schedule
In the diffuser tag, add a spot to list the diffuser neck size (so the duct runout doesn't need to be labeled and will clean the drawings up). It would be nice if one diffuser tag can be used for various diffuser neck sizes, for instance, a CD-1 is more of a description of the diffuser type and model and a pull down with diffuser neck size would be input, then the schedule can list CD-1 with a line for quantity of each diffuser size. This would make creating a master schedule much simpler.
We have features that address a lot of what is described here.
The callout format itself can be changed to include the neck size.
You can set the neck size to 0 in the schedule. Then it will be sized automatically based upon the airflow. You can lock the duct size if you want to force a specific neck size.
I think these two features that already exist will get you pretty close to what you are looking for.