Hi
For tiered dropdowns we structured the file system to align the option choices, so in your secondary options you would have a Remote URL something like:
file:/app/test/${option.name.value}/value.json
So you would have a file structure with directories A, B, C under file:/app/test and a JSON file in each folder for their respective values.
I don't know of a method to support the option to only display Option 4 though