As I mentioned in a post elsewhere in the forum, Connecticut already requires an ammo buyer to present a state-issued firearms card ... even if no actual weapons purchase is involved.
I don't know whether the gun shop just "looks at" the card, or if they're required to "record" it in some way (such as swipe a bar code on it), to register the purchase with the state.
But such things are "already here", at least in CT ...