I know.
Jackson has said that the TTT had the most deviations from the text, which leads me to believe we won't see much off the wall in ROTK.
Certainly his first priority must remain compiling a compelling cut of the film. That inevitably requires some compression and some excissions - and the odd change or two.
The debacles of the Clancy films represent one danger - fundamental changes to the point that little is left in common with the books but the names. The slavish faithfulness to the text shown by Chris Columbus in the Harry Potter films is the other.
Especially since slavish faithfulness to Tolkien would result in about 20-25 hours worth of film - excluding, of course, the appendices.