With our ID blocks in the top right of the window, the little + and x icons make the Blender UI overly busy and complex. There's also the problem that, at least on Windows and Linux, the close button is in the top right corner of the display, creating this clumsy configuration of two X's.
We could change these ID blocks to work as popovers instead, creating a much simpler top level interface. When opened, we can display the controls to add, remove or rename items inside the popover, similar to what we already do for the presets:
This would result in a cleaner top level UI, and avoid the double X on some OS's: