Re: DC's New 52: Reviews and Discussion (Spoilers welcolme and likely)
I don't think he plans to take on another book. Between JL, JLA, GL, Aquaman, and his job as head of creative control at DC, he has quite a workload. Leaving Green Lantern frees up some time for him.
"In Brightest Day, in Blackest Night, no evil shall escape my sight. Let those who worship evil's might, beware my power: Green Lantern's light!"