The Hobbit is vague about the evil sorcerer in Mirkwood (and goings on in the land in general outside of quest). They could expand on that as bridging information between the two, without changing what happens from The Hobbit itself. You can have something of Sauron directly or via his minions looking for the Ring without it wrecking The Hobbit by encountering the party.My understanding is that it is not exactly turning The Hobbit into a trilogy, but rather adding another film based on other bits and pieces of material written by Tolkien, as sort of a bridging film between the end of The Hobbit and the beginning of The Lord of the Rings.





