Who said you can't write your own rich text editor from scratch in #JavaFx. I made it for my side project. Now it will be even easier for others, because JavaFx24 already has an experimental component that handles this.
It took me several months (after day job) to create the first version. It is not a WebView or RichTextFx, I had to take care of everything from the scratch (how the caret should blink, how to navigate between characters using the keyboard, how the undo/redo action should be implemented). Even though it was almost a year ago, this is the part of my project that I am most proud of.
It may still have some issues, but you can check out how it works at http://keepmark.io/.