Did I spell it with one "L" again? DOH!
Jeff's main concern has always about the integrity of the story and characters, not anything to do with himself or being a diva, and Kevin out of respect for Jeff knows this. He loves these characters just as much as we do, if not more, and doesn't want Kevin just doing something for the sake of doing it, which Kevin has talked about in the past as a concern. That's why Jeff is the potential end all or be all of this project. I really don't see it happening without him.
Those who have heard the pitch (and it's only really like four or five people now) have said it's the best thing that Kevin's ever come up with (outside of "Hit Somebody" which he himself has said is his best work writing wise).