The prerequisite would be experience and willingness to run a pro style offense. I'm not sure at this point. I don't believe we'd promote from within, but who out there (in college) isn't running some variation of the spread. I'm not saying there's anything wrong with the spread, but Saban has mentioned a number of times his willingness to put players in a position to exceed at the next level, and to be quite frank, the spread doesn't exist in the NFL.
Would he go after a current NFL assistant?