fltk-rs would be a very good GUI choice for multiple reasons:
you can use fltk-egui to support egui running inside FLTK.
It is compatible with both x11 and Wayland on GNU/Linux systems, as well as Windows, Mac and AFAIK android
It is much smaller and lighter than GTK/Qt while providing a very competent GUI toolkit
FLTK is very fast and fully themable
FLTK is used in zynsubaddFX already
FLUID is a great way to make a mockup design for the UI/UX
fltk-rs is well supported
There are so many sub-libraries available such as a theme library, is easy to extend for custom widgets like the extras, accessibility, and can wrap virtually anything like webkit and VLC for demos or documentation
That's definitely an interesting suggestion. I think the team was leaning towards either egui or iced, but definitely a good option to have on the list.
fltk-rs would be a very good GUI choice for multiple reasons: