Mild spoilers if you haven't read the book
After seeing all three Hobbit films I feel like even though it is a simpler book than the LOTR trilogy it is the real unfilmable chapter in the series. Say what you want about stretching the film out into 3 movies, as a filmmaker I would probably make the same decision because Tolkien wrote a literary trap for film makers.
The reason LOTR was supposedly unfilmable was because of the sheer amount of content. But the core nugget in the story is pretty simple, there is a powerful weapon and the characters have to get from A to B to destroy it. Along the way the characters branch out and the world expands but the goal is still singular. All the action is based around how people are affected by this weapon good or bad, so really the only limitation to making it is you need time and money.
The Hobbit is different, on the surface the story arc is very similar. A group needs to go from A to B to reclaim a treasure. The problem is that the battle of five armies is in essence an act 3 bait and switch. This story that is supposedly about this hobbit's personal journey and growth all of sudden becomes an afterthought amidst the political gamesmanship of Gandalf v Sauron. The novel also gets away with a lot of this by giving us explanations after the fact from Gandalf or just not filling in the details. That type of exposition doesn't work in a film though.
So the question becomes do you cut the battle from the film and make the showdown with Smaug, which is the natural climax to the adventure story, the new ending or do you try to justify the battle. Peter Jackson went with the second option and it works as well as it can. The problem is all the exposition to justify the battle is scattered throughout the previous films in the form of the Gandalf B plot and if you don't already know what those scenes are building towards the film it's hard to put all the pieces together in the moment. Especially over three years of films.
So that's the problem. Is there a solution? I'm curious how two films would have worked. In the making of Smaug Jackson basically admits by stretching it to three he no longer had an ending for the 2nd film. I'd like to see what it would look like if you killed Smaug by the end of the first film (or at least the second) and moved all the Gandalf scenes into the the start of the third. By honoring the narrative arc of the book I think you are hurting the emotional arc of the film. If the final film contains the entire emotional arc of the battle of five armies, which is really Thorin's and Gandalf's story, I feel like it might be able to capture the power of LOTR. Or maybe not, it's hard to say but I'll be curious to see the recuts that appear online.
I do have to give Jackson credit for making three entertaining films. His visual gags are second to none for their creative energy and visual wonder, as ridiculous as they might be. I would love an emotional core that is just as strong, but for all the reasons I discussed, I just don't know if it's doable. The Hobbit seems simple but in many ways it's the most complex narrative of the series. Unless you take on the Silmarillion, then frankly you're just fucked.