Again, more details than someone with my experience should be fully involved in this deliberation. But I shall provide my two cents worth.
When I was doing a little research for the original article, I ran into a little clip that Canada has already instituted a user license of some kind. Because I am not a firearm enthusiast, I cannot verify this or give you exact details. But it seem Dave Tomlinson's ideas are somewhat in place.
My brother is a farmer. When he has some spare time, he drives out to the prairie and shoots gophers. He believes that overpopulation of gophers will eventually eat his crops. He is probably right.
He has a 22. He is not a game hunter. He does not have a license. It is unlikley he would get stopped. And if he did, the police/game wardens would likely issue a warning than enact some kind of penalty. They might even let him continue with his hunting without putting his name in the system.
If he needs to get a 22 license, it should be a simple matter for him. He has been shooting gophers for 50 years!
As there are different grades of firearmes that could justify different kinds of firearm licenses, there are also different grades of mental illnesses. To deny access to all firearms because of a minor mental illness (which I have) seems like overkill to me. And in minor cases, mental illnesses are probably best not reported to the whole world. And if a person has no interest in firearms, why should they have their mental illness exposed?
Unlike firearms, the grades of mental illnesses are not as easily defined. There is a lot more subjectivity here, which is way an appeal process is important. I can see such a person being granted a license for less lethal firearms.
That's my two cents. I don't think the "everyone must get a license" will work.