Okay, so, things seem to be actually rolling with this gigantic three movie, two TV series adaptation of SK's Dark Tower series (produced/directed by Ron Howard and hopefully starring Javier Bardem as Roland and Naomie Harris as Susannah Dean, but time will tell), I've started re-reading the books. I've started having thoughts about what I think is going to happen, so I figured I'd try writing them down here to see how I hit the mark in a few years:
1) We know they're seven books plus a series of comic books and short stories divided into three movies and two series of what I'm assuming will be network television: Movie 1, TV 1, Movie 2, TV 2, Movie 3. My guess at the division:
First Movie: The Gunslinger
First Season: Drawing of the Three & The Wastelands, with non-flashback bits of Wizard & Glass interjected somewhere outside of book continuity. Probably between Jake's re-emergence and their arrival at Lud.
Second Movie: Wolves of the Calla
Second Season: Flashback bits of Wizard & Glass, plus bits and pieces of the comic book series. Maybe Wind Through the Keyhole if it exists by that time, and Eyes of the Dragon and Little Sisters of Eluria if the rights come with the series.
Third Movie: Song of Susannah and The Dark Tower.
2) The crossover aspects will be reduced if not completely eliminated. My guess is buying the rights to The Dark Tower does not buy the rights to the other Stephen King books and characcters referenced in the series. Any reference to Captain Trips will be gone. And as much as I would love to see Jamey Sheridan, James Cromwell, and Anthony Hopkins return to their previous roles, the histories of Flagg, Callahan, and Brautigan will be altered, if not completely re-written, to eliminate any connection to The Stand, 'Salem's Lot, and Hearts in Atlantis. Dinky Earnshaw, too.
Non-SK references will be eliminated, as well, unless it's public domain. We may still see the Emerald City, but Shardik will be gone (at least by name), and the sci-fi-mashup Wolves will look completely different than their Fantastic Four/Star Wars/Harry Potter book counterparts.
More importantly...
3) The role of Stephen King will be written out completely, which might be a blessing in disguise. As interesting as the concept is on paper, his job of creating the universes just wouldn't play out as well on the screen. Also, the movies will be trying to embrace a completely different audience than the books. A non-SK reader suddenly given the introduction of the writer himself as a major character... well, I think the words "Are you fucking serious?" would be a reasonable response, and one you never want to hear as a movie producer.
King's disappearance also means:
4) Jake's death will be different. Even if King does appear in the series, Jake's death while rescuing him from the van accident would NOT go over well with a mainstream audience. Hell, I'm pretty sure it didn't go over well with the readers. If Jake dies (the third time), it will be in a different way. My guess is his second death will be different, as well, since...
5) Roland will get a "Greedo Shot First" transformation. It may be one thing if JJ Abrams were still involved in the adaptation, but I doubt that Ron Howard and company will let Roland choose to let Jake fall. It may be an accident, it may be Walter doing something to the boy before Roland can stop him, and Roland may still continue to blame himself for it, but it won't be "Roland chose The Tower over The Boy" like the novel states.
In addition, The Battle of Tull will be different. In The Gunslinger, every townsperson is hypnotized to attack Roland. No way Howard (or the studio) is going to let their major hero gun down children, mothers, and old people, no matter how rabidly homicidal they may be. They may re-write the attack to only include adults, or they may twist the town around so that children aren't there (the world has moved on), but it's not going to happen the way the book says it.
Worst case, Roland may tweak his plan of attack to include a lot more non-violent methods. Which would be unfortunate, since it's the character's first "THIS is what a gunslinger is about" moment.
Beyond Tull...
6) The series will be toned down in general. Universal's the studio, and it's almost assured that the series will be on NBC (as opposed to one of their cable networks like USA). That means the series will be network-standard for language, violence, and sexual content. In order to keep the audiences coming back, the movies are going to have to be held to the same standard. As much as hardcore fans will hate it, there's no way the three movies will be R-rated. PG-13's the best guess.
7) No, seriously, TONED DOWN. Detta Walker will be a shadow of her former self (no pun intended). It's easy enough for a book character to listen to her and think "huh, she's like a caricature of some African-American stereotype, straight out of Amos & Andy or Butterfly McQueen", but it's a lot harder to put that thought into movie dialogue. My guess is the shift between Detta and Odetta will be much more subtle. Or, on the other side, they might make Odetta more of a caricature, an innocent akin to Amy Adams in Enchanted, while Detta becomes more of a quiet serial killer type.
8) Finally (for now), they'll give us both endings, pre- and post-credits. Pre-credits will end with Jake and the Deans living happily ever after, post-credits will be the Roland-In-The-Tower, Reboot-It-All ending. That way, like the end of Dark Tower and the end of Deathly Hallows, you can pick whichever ending you prefer.