It really isn't a new rule, they have had the same position that parts intended for use in a suppressor "are" suppressors ever since the whole Diversified Machine debacle. It is odd that they sent that memo out to dealers at this time, I have heard theories that they are in the stages of a new enforcement effort (ie, about to go after more dealers and suppliers), that this was not an intentional notification and that the memo getting sent out was either a system feature or flaw and even that there is someone inside the ATF that is on our side pushed this out at this time in an attempt to get the ATF drug into the Administrative State / pistol brace / bump stock ruling cycle.