When the USA eventually works toward sensible firearms legislation, a lot of these points will be needed to deliberated on. Your vision could be the vision eventually implemented.

No one knows how they will confront an out-of-control shooter until they are faced with this situation in real life. If the shooter has a 22 rifle, I hope I could convince three or four other people to charge him. At best, he might only hit one of us before we take him down.

But an AR15, that's a whole different story.

Sorry, firearms are not the same. Just as mentail is not the same. A lot of deliberation will be required to get a "user liscense" to be effective.