Peter Jackson already had enough on his plate with The Hobbit, making some four or five hours worth of epic fantasy fare, full of complex effects, dozens of characters, and several elaborate, full story arcs. Adding in the newly-confirmed third film is just going to make the swamp deeper, and he'll have to wade even harder.
According to The Hollywood Reporter it's estimated that the third Hobbit film will cost something like $125 to $170 million, though nobody actually knows just yet. And that's because there's no script for this third film.
Jackson is up to his knees right now, shooting inserts and pick-ups for battle scenes in the first film, and then he'll be busy with post production. It's likely to be at that time, in parallel with the editing, that he'll convene with Fran Walsh and Phlippa Boyens and try to get the third script nailed down.
Maybe then they'll be able to finally decide on the title they're going to give it – obviously something very important, right? You can tell, by the volume of articles I've written about it.
So. At the other end of the To Do List, with a big fat line through the middle is "Make Some Special 3D Glasses To Release With The Film."
Here's an image of said glasses, courtesy of Hobbit Film.
I'll stick with my old faithfuls, I think.