In my construction of "reasonable" ...a person could have almost any weapon they want.
Your CCW model is similar to something I've proposed. It goes like this ...
1) I think we can classify weapons based on how lethal they are during any given usage. And the elements of this could be quantified. You would use metrics like ...
a) Shots fired per minute.
b) Number of shots fired without reload.
c) Damage done to a human target from 3 feet, 10 feet, 20 feet, 100 feet.
And so on ... I'm not suggest these 3 specifically, just using them as examples.
2) You could do the same for various types of ammo, some of which is designed specifically to deform or fragment to increase the damage to a human target. Again, develop some metrics.
3) Graded Gun licenses. CCW is kind of an example of this. To be able to get a CCW, I have to prove proficiency. I think we could do something similar for some of the more lethal weapons. You want an AR-15, no problem, pass a (periodic) test to prove you can safely handle that weapon.
Then let's get creative ...
Take a gun safety class, get a tax break, or a discount at Walmart.
Turn in a weapon that falls outside the ranges, or donate it it to local police, get money back. Hey, give it to the local gun club, and they give you a discount.
I like what you suggested, and I think you prove that we can find creative approaches that, while they will never stop all gun violence, they could help people do what many would say is critical to gun safety ... "respect the gun".