Dominic Monaghan has said to MTV that he is in informal talks with Guillermo Del Toro about seen the original hobbits (actors) return to play in the two new Hobbit films.
He said that Del Toro wants to say thanks to the original actors by way of this and thinks that the fans will love the idea. He hasn't said whether he is splitting the Hobbit book into two sections or whether he is making the first one the Hobbit and the second movie into a Hobbit "1.5" to bridge the story between Bilbo's tale and Frodo's. Details are hard to come by so its difficult to tell what will be what at the stage.