One could just use OpenGL like Blender does to great success, maybe add something like Kivy on top. "Native feel" is not really the most desirable feature for a graphics app, especially since both (1) Linux users are used to non-native looking stuff (even Qt in GTK or the other way around is always at least a bit off) and (2) most native-looking apps, especially the GTK ones, have horrible UI/X, hence users don't tend associate "native looks" with "uuh, this is gonna be a smooth experience" (like Windows users are used to).

(Also, anything that move people even the slightest bit away from Gnome and GTK is a win my book ;) They may feel like the standard now because of Ubuntu, but imho the people working these technologies are totally tone-deaf to what constitutes good UX/I and they are moving further and further in the totally wrong direction... Thank god we have KDE/Qt, and Xfce if you need some "retro but sane" experience in the Gtk camp.)