I seriously doubt there will ever be gun confiscation in the US short of the red flag laws, where a specific person who is deemed dangerous by a court can have their guns confiscated. https://www.cnn.com/2021/04/21/us/red-flag-laws-explainer-trnd/index.html
First off, any straight off confiscation would be unrealistic for a myriad of reasons. The closest the US would come would be mandatory buybacks, but again, those would be difficult to enact. The mandatory buyback comes from Australia which has a stricter "takings" provision in their constitution than the US does. Takings being where the government can acquire private property for public use. The Fifth Amendment of the United States Constitution mandates that if the government takes private property for public use, the government must provide "just compensation." Typically, a "just compensation" is determined by an appraisal of the property's fair market value.
Now, just imagine how much it will cost to buyback the firearms of anyone willing to turn them in for a fair market value: i.e., bluebook cost.
Sorry, not illegal or unconstitutional since buying back is provided for in the US Constitution, which is something people claim to believe in. Yet they have no idea what it actually says.
The main factor in getting people to turn in their guns for payment would be criminal prosecution and that any amnesty after the buyback period would be a definite turn in your guns for nothing. Well, the something would be that you wouldn't be prosecuted for having it.
Another option to a buyback would be mandatory registration under the NFA. Any luck the registration would be less expensive and not as restrictive (e.g. not requiring someone to sell the gun in the registered state or go through a lot of paperwork to do it).
That means your choices would be: register your firearms, sell them back to the government for a fair price, or run afoul of the gun laws and never have a hope in hell of ever owning one legally.