I wonder whether this requires particular GUI toolkits to be used, such as WFC. In any GUI there are enough "bad boy" toolkits which just "draw lines" and thus are not accessible at all.
The coverage varies by toolkit. Win32/WPF/GTK expose rich trees. Electron apps expose key elements but the tree is shallower. Custom-drawn UIs (games, OpenGL) have minimal or no accessibility tree. That's the main limitation.
