If you are developing a UI framework for JavaFX, then please make it a habit to always split your custom controls into a control class and a skin class. Coming from Swing myself this was not obvious to me right away. Swing also uses an MVC concept and delegates the actual component rendering to a UI delegate, but people extending Swing mostly subclassed one of its controls and added extensions / modifications to the subclass. Only very few frameworks actually worked with the UI delegates (e.g. MacWidgets).
I have the luxury of being able to compare the implementation of the same product / control once done in Swing and once done in JavaFX and I noticed that the JavaFX implementation is so much cleaner, largely because of the splitting in controls and skins (next in row: CSS styling and property binding). In Swing I was exposing a lot of things to the framework user that I personally considered “implementation detail” but that became public API nevertheless. The JavaFX architecture makes it much more obvi