Music cred: Popularity-wise? Fergie's got ample credibility. But is that really credibility? Do the kids think of her as being a top-notch recording artist? Or is she just a loud singer who gets upstaged by will.i.am and famously peed her pants once on-stage?
Why he/she would be good: Fergie would bring energy and popular credibility to the panel, plus a fair amount of cross-over success in different genres and even into acting, kinda. With her "Kids, Incorporated" experiences, she may actually be a terrific mentor to young performers.
Why he/she could suck: She'd have to want to mentor. Nicole didn't really seem to want to mentor. She'd also have to want to judge. Nicole didn't really want to judge. The jury would be out on Fergie's desire to do either of those things.
Chances: Would Fergie be willing to settle down for three months to concentrate on "X Factor"? We don't know. But we do know that she once appeared on an episode of "Mr. Belvedere." 15 percent for that alone.