That comparison is pretty weird. Electron is more extensible than JavaFX? How does that work? Browser engines are not exactly famous for their sophisticated API extensibility or advanced text/graphics APIs.
I love JetBrains products and their approach. If I had any interest in writing Java (or desktop) I would love to work there and be part of the mission.
I like their approach, too. Just by looking at this project GitHub page, one can clearly see the list of supported features and not yet working/planned, which is essentially all I need from such a project. Seems obvious, but very few projects realize this/care enough to make it crystal clear like JB did.