In all likelihood, this won't get off the ground. They've been batting a Shadow of the Colossus movie around for years now, and the project never seems to get its footing. That's pretty common for these big titles nowadays. Publishers are getting more protective of their gaming properties; it's why a Halo movie (which seems much more likely) still hasn't seen the light of day. Look for this one to start floundering as soon as a new screenplay is submitted.
Hypothetically speaking, if it goes forward, I'm at least glad that the director seems to know the source material. Well, that's what I'm guessing, since he specifically asked for the project. I wonder about how it would translate...you obviously can't show all the colossi battles due to time/redundancy issues. What works so well for the game as an interactive medium certainly doesn't pack the same punch in movie form. 3 colossi seems like the sweet spot to me.
The head priest and the dormin can provide most of the exposition just as they do in the game, but I'd say the movies success would hinge on how artsy they're able to push it. Definitely keep the dialogue to a minimum. Lots of still, contemplative moments, and shots of the landscape.
That's a tough sell. A movie like that likely wouldn't get the box office numbers to justify the high costs that would be needed to make it work.
What colossi would everyone like to see? My votes go to
Gaius,
Hydrus, and
Phalanx. Gives you a nice "ground, water, air" combo. I don't necessarily think they'd have to end with
Malus, as they do in the game, if they made one of the others a bit darker and more imposing to play the role of "end boss".