http://collider.com/scott-stewart-interview-priest-mortal-instruments/84415/#more-84415
Last update I've seen had them trying to start production in March 2011.
Here is relevant dialogue after they discuss Priest 3D:
- 6:39 Talks about being attached to direct Mortal Instruments. “We’re hoping to get ready to shoot late-summer early-fall. [We’re] working on the script right now and casting. We have Lily Collins attached to play Claire Fray, which we’re really excited about. We’re in the midst of doing a bunch of designs for the vehicles and the weapons and the creatures and the world, and we’re trying to figure out exactly where we’re gonna shoot and all the good fun stuff.
- 7:19 How does Mortal Instruments compare to Priest with regards to scale? Is it bigger?
“It’s actually a little bigger, but it’s a very different kind of movie. I mean it’s a “set in New York” movie it’s not a “takes place in an entirely new world.” You know Priest is an entirely alternate world, and everything in the movie is designed. New York is a big character in the movie, I grew up loving those “New York at night” movies like After Hours, where the sun goes down and strange things happen and adventure is there, so that’s an influence. Movies like The Lost Boys is an influence, that sort of sun goes down movie. And there’s a kind of sexuality and sensuality and excitement. And so that’s something that we really wanna try to make a part of it, it’s kind of a very different thing stylistically. It’s also a really music influenced movie, and so that’s something that’s gonna be really fun, a chance to integrate a lot of contemporary music into the movie.”
- 3D or not 3D? “We’re actually shooting in 3D.”