Do you mean that this “continuous development” of gnome-shell is actually a hindrance to 3rd party developers?
No, this means that GNOME don’t want to have a global menu, they also don’t want to have a menubar (a global menu is a menubar that we export on DBus) and more than that, they consider a menubar as an obsoleted concept and then is something not recommended to be used in applications. So, the GNOME flow is in the direction of remove all possible support for that type of things.
But yes, it’s much worse now, because the only opposition to that tendency in the desktops with base on GNOME technologies was Ubuntu with Unity, but now is discontinued and not only that, Ubuntu developers are now part of the GNOME community and in concordance they are accepting the GNOME HIG. That means they also accepted that:
Menu bars increase the vertical footprint of an application’s user interface, introduce a large number of disclosure points, and function as a fixed set of inflexible options. For these reasons, header bars and header bar menus are generally recommended over menu bars, along with other design patterns for exposing controls on demand, such as selection mode, action bars, and popovers.
So, now the river flow of the Ubuntu developers is in the same direction that GNOME and then build a global menu in the Ubuntu desktop that is constructed with the GNOME technologies is like swimming against the river flow. I hope this is more clear now.