Subsequent to Lopez, the "new and somewhat improved" GFZA was passed with certain amendments that made a feeble attempt at recognizing States' rights. These amendments were put in place prior to most States having CCW and/or reciprocity with other States. I think some good arguments can be made that a permit recognized from another State is as good as a permit issued in that State, but I do not think this issue has yet been tested.
I do think that any attempt at nationwide restrictions on CCW would be met with a wall of State sovereignty suits.