Well, presumably they just need to provide SurfaceFlinger backends to Qt and Gtk. AIUI, SurfaceFlinger basically gives the app a buffer and an OpenGL library, a

Well, presumably they just need to provide SurfaceFlinger backends to Qt and Gtk. AIUI, SurfaceFlinger basically gives the app a buffer and an OpenGL library, and the app handles the drawing itself; this is pretty much how Wayland works, and how GTK and Qt on modern X servers work, too. So it's not clear to me that porting to SurfaceFlinger would be such a huge amount of work (no more work, anyway, than porting to Wayland).