Ellison's only sued when he's had some slight form of proof at least. He's at least had his name on a story or script to use as evidence in his previous cases. An idea at a pitch meeting isn't very stable grounds for a lawsuit.
I'm not saying the case is strong. However, I could see Ellison arguing that he "published" his idea by allowing a synopsis of it to be included in King's book where it could be seen by, among others, Abrams and the writers of the current film.
As mentioned before, he's a pretty litigious guy.
