I think this represents what is wrong when hollywood gets ahold of an idea. The assumption is that the movie needs a romantic storyline. I would argue it does not, what it needs is an emotional storyline. Why is passion for another person the only passion that hollywood assumes will sell?
Reminds me a rumor (I hope a rumor) that due to the success of The Dark Knight, hollywood is looking to make the next Superman movie darker and grittier. Dark worked for Batman, so it must work for superman! Nope, wrong again. This is a failure to work with the source material and keep the characters as who they are.
The lord of the Rings is not the Hobbit, or vise versa. Trying to put in a new, ungrounded storyline would greatly alter the work. They may have added much of Aragorn/Arwen's love tale into LotR, but the story was grounded in the appendicies. Tolkien wanted the storyline in but had difficulties working it into the rest of the narrative.
The hobbit? Yeah, not so much.
Who knows, maybe in a serious wack to our collective cerebrums they will show a love story with Denethor and his wife, to culminate with her death when Faramir is born. Making the viewing audience much more sympathetic for a character who hates his son so much in Return of the King. Perhaps not hate, but surely does not appriciate him. Love and loss, now that's a tale Hollywood can get behind.