From Bearing Arms:

The Supreme Court’s decision to scrap the Chevron Doctrine doesn’t automatically mean that the ATF’s rules on unfinished frames and receivers, pistol stabilizing braces, and who is “engaged in the business” of dealing firearms will be thrown out by the federal judiciary, but it definitely makes it more difficult for the DOJ to defend the rules going forward. 

No longer can the agency reliy on judges giving the agency the benefit of the doubt when it come to interpreting supposedly ambiguous language. Unless the ATF is strictly adhering to the underlying statute when crafting its rules (which has not been the case in recent years) the odds are good that the rule will fall.