From my perspective, I don't think "the goal is for r/g to stay simple above all".
Being cross-platform definitely is an important goal for racket/gui.
That said, there is also room for incremental improvement. For a recent example, a way to react to switches into or out of dark mode was added in add application-dark-mode-handler · racket/gui@9682a95 · GitHub, initially only on Mac OS. GTK support was added in Update gtk to react to dark mode changes · racket/gui@223e609 · GitHub a week later, and, for Windows, Dark Mode under Windows · Issue #197 · racket/gui · GitHub is still an open issue. If you can implement a feature for one platform, others may be able to fill in support for the rest. Of course, before you put in too much time on a patch, it may be worth checking with others that your approach sounds reasonable and doesn't pose any avoidable issues for other platforms.
I'm interested in examples of missing features you'd like. I've found racket/gui very useful for cross-platform desktop apps, though of course I have pet peeves (e.g. Scrolling `racket/gui` panels with the mouse) and wishlist items.
If you aren't aware of it, Framework: Racket GUI Application Framework has a lot of additional functionality implemented on top of racket/gui. (This manual has a lot of room for improvement!)