I think the next coach (if reasonably unproven) needs to have served (in any manner, including time as a GA) under multiple great football minds. This seems obvious, but you'd be surprised at how many head coach hires don't fit this bill. Saban was a coach under (most notably) Don James, Earle Bruce, and Belichick. Urban served under Earle Bruce and Sonny Lubick. Kirby Smart served under Bobby Bowden, Mark Richt, and Saban. When I look at potential candidates, two that fit this bill come to mind: Brent Venables and Mel Tucker. Venables has served under Bill Snyder, Stoops, and now Dabo. Mel Tucker has served under Saban, Jim Tressel and now Kirby.
Looking at past great hires by other programs, this holds. Pete Carroll served under Lou Holtz and Bruce. Bob Stoops served under Hayden Fry, Snyder, and Steve Spurrier. Mark Dantonio served under Bruce, Tressel, and Saban. Lincoln Riley served under Mike Leach and Stoops. Jimbo served under Saban and Bobby Bowden. Les Miles served under Schembechler and Bill McCartney.
Of course this prerequisite doesn't always mean a coach will pan out. Charlie served under Lou Holtz and Urban Meyer. Weis served under Parcells and Belichick.
Sometimes, a guy who pans out never served under anyone notable. Such coaches are Gary Patterson, James Franklin, and Mack Brown.
The only notable coach Herman served under is Urban Meyer. I'm thinking we should stay away from the Urban Meyer tree from now on.