The suddenly impressive tailback depth would help Peterson, too.Of course, there are a few major hurdles here:1) The dip in running back production at age 30 is significant (a drop of 100-plus yards on average from age 30 to 32).2) Peterson could veto a trade to a place such as Cleveland, which doesn???t have Dallas' cachet.3) The Vikings might not trade him.Those last two points are unavoidable.A