I was a little bummed to see this was not using Kotlin and TornadoFX, I've used them together a little and they're much more pleasant than using plain Java + JavaFX.
I find myself dipping into Java code a lot, and mentally translating examples from Java even more, with TornadoFX, particularly with regards to XML Scene Builder and databinding. K+T are very pleasant, but the docs have a ways to go