If someone submitted a patch that ported everything in GIMP to GTK4, I'm quite sure it'd be accepted after review. The trouble is that GTK4 deprecates or breaks

If someone submitted a patch that ported everything in GIMP to GTK4, I'm quite sure it'd be accepted after review. The trouble is that GTK4 deprecates or breaks a number of things as well. For instance, while the icon scaling system is much more flexible in GTK4, it's different than in GTK3 so all that work would have to be redone. GtkTreeViews are also becoming obsolete, and since GIMP relies on that for the layer/path/channel views, it'll be another big change. At the moment, new development is encouraged to follow the GTK3 -> GTK4 migration guidelines (e.g. use gtk_widget_set_visible () rather than gtk_widget_show (), don't use gtk_widget_destroy () since it's been removed, etc). I don't know a specific issue tracking GTK4 at the moment, but I can check.