Personally, I would have no problem with this rule.
I have always thought it was entirely stupid to penalize a defender whose hand merely grazes the facemask with no grabbing at all, but a RB can push his hand under the bottom of the facemask and hold it up with the defender's neck pressed back while he runs ten yards.
Emmitt did this lots of times...running down the field while essentially holding a defender's facemask.
I'm sorry, but I think that's a stupid thing to allow the RB when the defenders get penalized for letting their hand touch it.
Stiff arms are often applied to the top and side of the helmit and to the shoulder or chest...a RB doesn't need to be able to facemask any more than a defender does.
I have no problem with a rule that would tell a RB he can't shove his hand in a defender's facemask and just run down the field while holding the tackler's head back.
You can call it a sissy suggestion if you want, but I think this inequity of rules is far worse than the overprotection of QB's or the raping of DB's in order to produce more scoring by the offense.