There is, I hope, a simple way to improve the jQt IDE UI, by replacing the tool bar icons.
I’m considering free icons under MIT licence:
https://icons.getbootstrap.com.
They have a modern look and could help showcase the language.
If possible, also refine horizontal/vertical alignments of the headers and tool bars, and ensure that fonts and graphical elements look either exactly the same or clearly different (I’m trying to attach a picture to this post to illustrate this).
I hope these are simple ways to make J look even more appealing, but I know UI frameworks may have limitations and this might not be a priority.