Well I have heard nasty rumours that the whole fight against the Corsairs is being left out, although it was mostly told in flashback in ROTK. I would think that it is easier to leave it in, to explain the absense of Aragorn and most of the Fellowship from most of the Siege of Gondor, and they have to be absent, or the whole plot structure is warped beyond recognition.
Bad enough that they are apparently leaving out the last quarter of ROTK. I have seen pre-movie analyses that the Scouring of the Shire is one of the main lessons of LOTR, the dreadful costs that must be borne by those who fight for the right, that much of what you are fighting for will still be damaged, though not totally beytond repair.
I didn't know he was leaving out the corsairs...that's interesting. I still think he'll include that great host of ghosts though--the creep factor of Aragorn, Gimli and Legolas being followed by that crowd of ghosts is surely too tempting to pass up. I wonder if he'll just have the spectral army show up at Pellenor Field and combine those two elements together.
Ack, I should never try to figure these things out, I always guess wrong, and I drive myself crazy in the meantime!