We already have that, Skans, it's called the Second Amendment, and it would take a supermajority of state conventions to change it.
Meanwhile, you'd exchange universal background checks for the promise that the antis would not use such to create a registry, and confiscation framework?
Sounds like promises frat boys make to sorority girls...
Honestly, I don't know. Believe me, I'm not trying to convince anyone that universal background checks is a good thing or should be any kind of acceptable compromise. I'm just exploring this through discussion, that's all. I don't see the antis ever repealing the 86 or 89 bans or agreeing to some kind of super majority on more confiscatory laws, so I don't know if it really matters.