Currently the U.S. is the only country in the world that calculates its import duties based on the FAS value of goods imported. Every other country in the world calculates import duties on the CIF value of goods. The difference between the two is the FAS value is determined at the port of export exclusive of shipping costs while the CIF value calculates duties on the value of the goods plus the cost of shipping. Such a move would level the playing field a little more.
From an international political perspective it offers the advantage of allowing the tariffs to be raised without actually raising the tariff rates. It is politically more defensible internationally since the CIF value is universally used outside the U.S.