I'm not saying it's not happening, but I can't conceivably think of a single reason why Bill would go to such great lengths to get Sean the job. If he has to prop him up that much, he's obviously going to fail.
I'm beginning to think more and more that "Sean" is more or less a code word for his entire staff. He knows that none of the coordinators have a chance to get the job, and Sean does due to his age and name.
Sean will survive the transition in some capacity because of his name. It may be a cushy job in the AD or something, but he'll be fine. But Dana, Seiler, Coleman, etc. will be cast out to the wind. Administrative staff? Gone. If Currie goes outside the "family", there's a strong chance that all of these cultural/legacy things he's tried to build will simply disappear. I don't think he's comfortable with that at all, and I think Sean is probably the reluctant, dutiful son that's been tasked with taking over for his father so all of his people inside of the program, including people like Joan, are taken care of.
I mean it all fits together if you believe the rumors that Sean doesn't even want the job. I really believe that Bill is simply staying so everyone in his locus of control is taken care of. He's just sticking around so everyone can keep their jobs.