There's an interesting recent article on special teams coaches moving on to be head coaches afterwards which has some rather impressive names on the list - Marv Levy, Dick Vermeil, Mike Ditka, Bill Cowher and Bill Belichick.
There's a quote from Marv Levy which highlights the benefits of hiring a special teams coach - "You got to work in every aspect coaching and evaluating offensive and defensive players, I got to work with just about every position."
I know there appears to be a call to get in someone with head coaching experience, but I expect Gruden, Dungy & Cowher aren't interested in leaving their TV gig and the idea of getting in an experienced head coach who would be available (think Jeff Fisher or Marvin Lewis, maybe John Fox) really doesn't appeal to me. If Toub is the choice I'm OK with it.
There was another interesting comment in the article about hiring offensive or defensive coordinators:
"Excluding Harbaugh, there were 67 head coaches hired over the past decade who were offensive or defensive assistants. Sixty-four of them had play-calling responsibilities as a coordinator. The overwhelming majority of those with four years or less handling those duties failed as head coaches. The success rate of more experienced assistants was significantly higher."