Users want to add some minor customization for "Format Cell" dialog without changing most of its functions. For example, using their own zul page and adding some extra behaviors.
But in the current design, most variables in FormatCellCtrl.java are private, users cannot simply extend this class and add their custom logic. They have to copy and paste source code to rewrite, but this way is fragile when ZSS upgrade.
If we consider to support this, maybe other dialogs may have the same requirement in the future.