To go with what I said before:
To add to that, even if it has come from Jackson, I too am concerned that there will be enough there to make a solid third installment using the appendices from Return of the King. The details found there are largely very brief, and could make for a very disjointed film, and one which is based on conjecture and speculation from Jacksons production team. I feel the best way would be to take the current second film, split that across two installments, and add the extended story lines in through flashbacks/other methods. Even then I would be wary.