NetBeans engineers are working on better Java -> Java FX integration. You should be able to build NetBeans UI modules with Java FX and integrate them so with a Swing app. NetBeans templates and build process will be also enhanced to seamlessly compile the module.
The Java FX code is referenced in the XML-file - there is no difference to the "old" Java approach here.
A suggestion: it should be possible to use an adapter to load a Java FX (Folder) class with javafx.util.FXEvaluator at runtime instead the XML-file - it has already a declarative syntax.
Then you would be able to build the entire app with Java FX - without any XML. It would be also type safe.
Web Apps, SPA, PWA with vanilla Java Script (ES 6+), CSS 3 and WebStandards only. As simple as possible, but not simpler. See you at: (Progressive) Web apps, Single Page Apps and WebStandards airhacks workshops at MUC airport, Winter Edition
airhacks.fm the podcast:
Stay in touch: airhacks.news.