The move to govern by executive fiat is loud and clear. The ATF & DOJ will publish this new rule in the second half of 2024, with a proposal released "soon," according to a new report by the New York Times —which seems to have access to internal ATF policy.

Other details about the rule in the NYT report include:

Anyone who makes "a profit" from selling firearms, perhaps as little as $1, is to be prohibited from selling their privately owned firearms without a Federal Firearms License (FFL) or a background check. 

According to the report, anti-gun organizations are pushing ATF to limit the number of firearms sales a private citizen may engage in without an FFL. Currently, anti-gunners want to limit collectors and sellers to 5 guns or fewer. An Obama-era regulation would have set the threshold at 1–2-gun sales per person.  

Failing to register as an FFL holder will carry a penalty of up to 5 years in Federal prison and a $250,000 fine.