Being mobile doesn't require a separate category for the position. Mobility is factored into every player's overall grade.
A running back that is good on 3rd down, is just as good on 1st and 2nd down. Secondly, there are no FB rankings. If a player were a 4 or 5-star FB, they wouldn't be a FB.
As long as you can run and tackle, the coach will decide where to put you. Size doesn't make tackles. Think Deion Jones of the Atlanta Falcons.
All players will be assigned a position when they show up to campus. Players are graded where they most likely will play at the college level.
No such thing as a strong side or weak side defensive end. As any shift in formation can lead to you becoming the strong or weak side defensive end.
With the influx of international players, the pool is too vast to legitmately rank. The college gridiron is the best sorting field for the top kickers and punters.