Someone ported GTK3.
https://discuss.haiku-os.org/t/ported-gtk3-live/7687
Could we reuse the SWT’s GTK backend on Haiku?
There are many SWT based software, most of them also Eclipse Platform based. Eclipse is not only an Java IDE but also utilized by other to be a platform for many applications. Please have a look at:
So, IMHO, Eclipse is a big plus for the Haiku ecosystem.