The registry is a non-starter. A significant fraction of gun owners will see registration as a precursor to confiscation. A smaller fraction fear that the registry will either be public from the start or significantly breached within a short time frame, such that gun owners will be selectively targeted for harassment or burglaries.

Given what New York has done recently, I presume that a lot of gun owners will also simply refuse to comply with any registration orders. And, as usual, the black market guns will remain nigh-untraceable, especially among those who are barred by law from owning them.

The best you could do is a database of last-known locations, maintained entirely without cooperation by owners, that will probably consist mainly of business locations of licensed firearm dealers and crime scenes.