They paid him a boat load of money, of course he'll endorse it.
They are fundamentally changing the character of Roland. The whole point of the whole series (and the Childe Roland poem, per SK) is to show the dogged, unwavering determination of Roland. 10 seconds into the preview, you have Jake begging Roland "please don't abandon your quest, we need you to finish it." I don't care if they continue the story and the events look different than the book, but abandoning the key themes and totally reversing THE foundational character trait of the main character is unacceptable to me, especially if the reason is so they can just shoehorn the story into a Hollywood template (main character will save the world, main character becomes unsure if he wants to continue to make sacrifices, side character inspires him to continue, happy ending).
Hollywood has butchered almost every single good book they've gotten their hands on, and the end result is ALWAYS a shallow, predictable story that disappoints. The exceptions are when the producers and directors decide to adhere strictly to the source material.
And the whole "this is actually a continuation" bit is a cheap excuse to do exactly what Hollywood always does. Strip down a best selling story that millions upon millions of people already love and let the egotistical directors and producers "put their own spin on it." I hope the movie flops (like almost every butchered book does) so one day Hollywood might say "hey we make more money when we stick to the source material closer like LOTR Harry Potter and Twilight).