In the screenshot below, each chart comes from a different plugin and all of them (except the scatter chart, which I included just for fun) react in an animated way, i.e., the lines in the charts visibly move up and down, when data is changed in the Swing JTable:
All the charts you see above are JavaFX components. And all the rest is Swing.
Note: Click to enlarge the image to get a better view. Apologies for the large view being very grainy; that's because there's some bug with enlarged PNG files on blogs.oracle.com, so I had to do a GIF instead.
At least two things are illustrated here that you don't get from JavaFX. Firstly, the docking framework, i.e., each chart can be undocked from the main frame, even moved to a different monitor. Handy if you're a stock trader, air traffic controler, defence force specialist, and, oh probably, just about every user of a large app would find this handy. Secondly, pluggability. The end user (or you, as the provider of the app) can decide which charts should be included in the app. All you need to do is go to Tools | Plugins and install a new chart provider, which is an implementation of an interface made available by the app for registering new charts.
But the main thing illustrated here is that you can pick the JavaFX goodies that seem relevant to your existing Swing app and simply disregard all the rest. (Or, move to the other parts step by step over a number of releases of your app, i.e., it's not an "all or nothing" thing.)