Perhaps its too early to be speculating, but I am wondering what the cost will be.
Avatar has been getting progressively darker, I suppose, more appropriate for its aging audience. LOK is generally so much more darker thematically and theatrically than ATLA.
This reminds me of the Harry Potter series and how the themes get heavier book after book. I wonder if the LOK writers will put in a Cedric Diggory... if so I wonder with who.