It was actually King in the interview he and Seeley did with Newsarama after Grayson 1 came out:
Note the reference to "seasons" and "shows." Metaphors? Hopeful thinking? Certainly a sign that, as Alexander Luthor said on another thread, the Hollywood paradigm is growing very influential in comics.King: We're doing it season by season, and the first arc will have an ending. We've set up this plot with Dick Grayson under cover, and that plot, we have the ending in mind and plotted out.
And then there will be a new sort of mystery after that. So people don't have to worry that this is a sort of Gilligan's Island show where he "almost" gets discovered for five years. There's an end to each of these seasons, and it's going to be awesome.