I think that an application with GUI pipes should draw only what it is supposed to do; it should not draw status bar, tabs, scroll bars, buttons, menu bar, window border, window decoration, etc.

The application should print a status line into a pipe, and the window manager would draw the status bar below the window, removing from the application the need to draw the status bar.

The application should send the contents of its window into a pipe, and the window manager would draw the content in a window, removing the need for the application to draw a scroll bar and to fit its content into the window.

The application should have a socket to receive commands from the window manager. The window manager draw the buttons and menu bar. The user chooses an action in the menu bar drawn by the window manager, the window manager send this action to the application via socket, and the application does what it is supposed to do.

The application should have no URL bar or any kind of prompt. It would receive text from a prompt in the same style the surf(1) browser uses dmenu(1).

I think that GUI pipes are supposed to remove from the application the need to draw most of the things a modern application draw on its window, and pass to the window manager (or other software) the task to draw the interface to the user.

In my view of GUI pipes, the only thing in the window drawn by the application is the window content, the rest of the interface is drawn by the window manager or some other program.