Even back when it was the second Hobbit movie, the third Hobbit movie has always held the subtitle There and Back Again, based on the actual secondary title of Tolkien's book. But now New Line may be thinking of switching the name to the somewhat more exciting The Hobbit: Into the Fire.
The reason that site TheOneRing.net believes the change is happening is because they learned New Line has recently registered this very title, much as it did with The Hobbit: The Desolation of Smaug shortly after it was announced that the two movies would be stretched to a trilogy. The site offers a variety of potential reasons for the change, from it technically being inaccurate with where the third movie starts, or an homage to The Hobbit chapter title "Out of the Frying Pan, Into the Fire" but I think we can safely assume that as the film has crept closer to its actual release, the most authentic Hobbit subtitle is also its most boring.
Meanwhile, I'm holding out hope that New Line will pick The Hobbit: Citizens on Patrol.