There and back again was the sub name for the book, but the book itself covers his journey back in short order. His journey back was uneventful so can't be one of the films.
With LOTR jackson cut out tons and he rewrote the first half to suit the audience (the move to crickhollow, old man willow, tom bambadil) added and removed characters (glorfindel, erkenbrand, 300 elves at helms deep, explosives, how many were at helms deep again?, liv tyler did what?) and trashed some encounters (legloas and the nazgul on the river, eomer was in helms deep, the scouring of the shire, sarumen as sharky in hobbiton) So who knows the outcome of a 2 film hobbit. We can only guess
Bear in mind the hobbit was a kids book written after telling a story to the kids so is a different writing style, LOTR was written over 15 years because he had a story to tell. (half the initial cash was his afterall so it wasn't exactly because he was pressured into it)
As such in the hobbit, huge areas are covered in a few pages. (The detail isn't needed for a five year old) The battle of the five armies was as big as the minas tirith siege or the battle of the black gate, lasting hours and involving waves of enemies. So could be half a flim, just like the return of the king. Then there is the sacking by smaug, the battle of dale which is about two pages of the book.
But you have to bear in mind whoever writes it is american and won't care, understand or be thinking like a story teller, it will be written for the sceen on some old way of thinking. Such as the obvious. "How a female lead can be shoe horned in" to please hollywood. 14 dwarves, one wizard and a hobbit. **No women.**
And the silmarillion is technically 7 books (not all interlinked) over two ages so given hollywood it could be anything from a Tv show to an epic.
As well as the average american not understanding it, so hollywood won't care and would dumb it down so much as to be laughable. Imagine Lucien and Beren's love affair with angelina jolie and brad pitt, or worse, who would play Tulkas teaching the elves to fight? Laughing as he defeated morgoth. Or about how life was created from harmony and notes so that the symphony could be played. Only discord was played by morgoth creating evil.
Hope they make the film as at least it is then a film that isn't a comic book and I can enjoy the cinema, but as LOTR wasn't that close to the story I won't count on the hobbit being that close either and will enjoy it as a stand alone tale. (Hopefully they will at least use the same set for the trolls as the extended first film has)
I'll get my coat.