Hopefully Smaug will be a huge UCS set along the lines of the Death Star. Anything less will not do him justice. I too would like to see Bjorn, and a Tom Bombadill, even though he isn't in any of the movies.
As a big Tolkien fan since high school, I don't really like the liberties Jackson has taken with the story. But the movies are stunningly beautiful, so I do watch them. Lego has done a great job with these sets so far, and I hope the line continues for years to come, to the point that we have sets based on The Silmarillion. Who wouldn't want a Forging of the Silmarils set? :)