I want to customize the window menu, but unfortunately I can't, because it's not customizable…
So I tried to remove the window menu, which you can do, and create my own window menu.
But then you can't have the list of windows.
And reproducing the window menu is a tedious process in itself
It would be much more simpler, to be able to modify the window menu (and you'll stil get the window list)
As I'm not selfish, let's make all non modifiable menu customizable :-)
I see no reasons there are non customizable menus, at least for the the window one.