If and when the USA gets serious about sensible gun legislation, the user lisence will be likley offered as a possible solution. In the end, there may be one tier (as you suggest) or five to ten. Hopefully, the delibaraters

Even with this system, the bad guys will still find ways to get the weapons they want. The 3-D printers will be churning out parts for to make certain guns. But if the guns show up for reason, no license, no guns.

There will be needless firearms deaths with this system. We will need at least five years to see a statistical downward trend. If that trend is not there, then we'll have to try something else.