So far they have hired Stephanie Sanditz to write the screenplay, and they are looking for a directer right now! Even better would be if the next two books in The Mortal Instruments series were adapted. City of Ashes and City of Glass, the sequels to City of Bones, would film back-to-back if green-lit. If The Infernal Devices: Clockwork Angel is green-lit it would most likely be released after those two, but could start production soon after.
That means practically 3 years of Shadowhunter glory!!