King's novel is complex and truly massive, encompassing 1,472 pages in its trade paperback form.  First published in 1978, it tells the story of humankind's decimation after a flu-like virus is released from a containment facility.  In the ravaged, mostly empty wasteland that was once America, survivors make their way slowly but surely to Boulder, Colorado and Las Vegas, Nevada.  In the former is Mother Abigail, a compassionate leader attempting to forge a real community, and in the latter is Randall Flagg, an anarchic bastard who takes joy in destruction.

In 1994, the novel was made into an ABC miniseries directed by Mick Garris, as well as a Marvel comic series.  When the development of a film version became known, King publicly declared not only that he was not involved, but that he also didn't consider it very likely that the film would come to fruition. 

While promoting the Potter finale, Yates mentioned that he was considering the project at Warner Bros, the studio behind Harry Potter, but no mention was made of Kloves' potential involvement.  Apparently, The Stand will consist of multiple films; it would be possible to present an abbreviated form of the novel int two films, but three would allow it to be done justice. 

It's likely that the performance of Deathly Hallows has given Warner Bros the confidence in this approach.  Also, the studio likes to keep its blockbuster auteurs close to home, allowing Christopher Nolan and Zack Snyder to take costly risks like Inception and Sucker Punch between more sure-to-be-profitable projects.

Interestingly, Universal Studios just opted not to move forward with its own ambitious adaptation of King's The Dark Tower novel series.  That would've consisted of three epic films with two limited-run television series to serve as bridges between films.  Despite the efforts of director Ron Howard, writer Akiva Goldsman, and producer Brian Grazer, as well as the attachment of Javier Bardem to play the lead, Universal could not justify the expense. 

When that project collapsed at Universal, Warner Bros was bandied about as the studio most likely to acquire it, but it seems the WB had its collective eye on The Stand all along.  For obvious reasons, David Yates and Steve Kloves are huge assets to the studio, and if their deals come together, The Stand is very likely to actually become a reality.