There are about 16 million AR-15 owners in the US. There may be more than 40 million in circulation. The Washington Post surveyed 400 owners:
Paywall-free link:
https://wapo.st/3zmip4G

Of course, I'd like to see AK-style and AR-15-style semi-automatic weapons banned, but they are so popular I'm not sure the political will can be mustered for a national ban. What I would like to see more than anything is a focus on mandating federal licensing of all currently legal firearms.

I think mustering the political will for licensing is feasible with a concerted effort to do so, but it will require a massive, long-term campaign to combat the propaganda against licensing/certificates.

Licenses should require safety training and background checks and be limited to age 18 and up. In the UK. younger persons can carry a firearm with the following exceptions

If carrying on behalf of the certificate holder (who is aged 18 years or over) and for the certificate holders’ sporting purposes only
As part of an approved club or cadet corps
On a Miniature Rifle Range
Under the supervision of someone over 21 years old
When the shotgun is in a securely fastened gun cover so that it cannot be fired
Unless on private property with the permission of the land owner. It is an offence for someone under this exception to fire any missile beyond the boundary of the premises unless with permission of the adjacent landowner.

yup

And a license should also be required to purchase ammunition for the licensed firearm with reasonable limits. For example, in the UK they have higher allowances for "pest control" or target shooters.

Insurance policies don't pay out for criminal acts like someone shooting another person. Home insurance already covers injuries by an accidental discharge in your home or a hunting accident on your property, or stolen property if your gun is taken in a robbery.

What would a hypothetical new gun insurance policy cover?

including medical bills that taxpayers pay for

What you're proposing is a new federal tax on guns and ammo, not an insurance policy requirement.

I am sick of gun humping cowards, tax the FUCK out of them

https://www.insurancebusinessmag.com/us/news/breaking-news/compulsory-gun-insurance-bill-moves-forward-in-state-house-484049.aspx

I thought about adding a "Depends on the situation" choice, but I figured it would just result in a huge debate about what those situations would be. As it is, choosing "Yes" actually covers special circumstances, as in yes the general public should be able to buy them but there may be special circumstances (permits/etc.) involved.

IMO, the manufacture in this country or importation of semiautomatics, including shotguns and pistols, intended for sale to the public would be prohibited. Those guns already in possession of private citizens would be grandfathered in .Not going to happen though.

I just wanted to keep the question focused on AR-15s.

The Troy PR-15, for example.

And there are lever action AR's, like the Bond Arms LRVB.

Currently they don't sell much because semi-auto AR's are easily available, but they'd be sold by the millions once semi-auto AR's were banned.

The best way to address the issue is to tackle the easy access to high capacity magazines, IMO, along with universal background checks and red flag laws.