@jchildress I'm going to put up a plain JavaFX post on refactoring with fx:include tomorrow or Saturday. It'll be based on the "NestedControllers" section here
https://docs.oracle.com/javafx/2/api/javafx/fxml/doc-files/introduction_to_fxml.html#reference_elements
This relies on both an fx:id and a naming convention. I had to look over some old code to remember how to do this. Very painful. I also involve WeakReferences to get shared parent controller FX fields over to the children.