A good way to accomplish this without patching gtk is to make the open file dialog a dbus service that returns a file, and then patch elementary applications to use it. The benefits of this approach could be expounded by GNOME (and other environments) also providing an implementation of the file chooser, and therefore GNOME and elementary applications would use the environment's implementation and remain consistent. Does that make sense?
A good way to accomplish this without patching gtk is to make the open file dialog a dbus service that returns a file, and then patch elementary applications to use it. The benefits of this approach could be expounded by GNOME (and other environments) also providing an implementation of the file chooser, and therefore GNOME and elementary applications would use the environment's implementation and remain consistent. Does that make sense?