I think Unity should do the same as unity-2d i.e. if an app is creating stubs or is blacklisted in indicator-appmenu or appmenu-gtk hovering over its title should not show stubs, this should be done in Unity itself since indicator-appmenu is used in Classic Desktop Session and not having these fallback menus there would make the panel look weirdly empty.
I think Unity should do the same as unity-2d i.e. if an app is creating stubs or is blacklisted in indicator-appmenu or appmenu-gtk hovering over its title should not show stubs, this should be done in Unity itself since indicator-appmenu is used in Classic Desktop Session and not having these fallback menus there would make the panel look weirdly empty.