Blender (3D modeling & animation software) implements this cool thing when rotating/resizing objects: if the mouse cursor moves out of the window it reappears on the other side (enabling resizing/rotating ad infinitum).
I think a better way to implement that feature would be a mechanism for programs to temporarily enable off-screen mouse cursors. This should also track the position where the cursor would be if it had been clipped to the screen boundary as normal, and immediately return the cursor to that position when the off-screen mode ends. Note that the OS returns the cursor, not the application, so applications can't abuse this mechanism for repositioning the cursor.
I think a better way to implement that feature would be a mechanism for programs to temporarily enable off-screen mouse cursors. This should also track the position where the cursor would be if it had been clipped to the screen boundary as normal, and immediately return the cursor to that position when the off-screen mode ends. Note that the OS returns the cursor, not the application, so applications can't abuse this mechanism for repositioning the cursor.