Archduchess Elisabeth Marie Marries Future King Albert I

So I recently discovered that Archduchess Elisabeth Marie sought, and nearly married, future king Albert I of Belgium. Leopold II disapproved due to the recent morganatic marriage of his daughter Stephanie. Say Stephanie does not marry again, forever scarred by the venereal disease that Rudolf gave her. Leopold relents to the marriage of Franz Joseph's granddaughter to the future heir to the Belgian throne. What effect does this cause down the line, in particular WWI as a Habsburg is married to the Belgian king?