Curious how those sources are saying that. The last time the ATF discussed it publicly they specifically said grandfathering. That is the precedent set in the original firearms act. There will also be a lot of lawsuits countering the act based on how they redefine the terminology to suit their agenda. No matter what happens it will be a shit storm for quite a while.
* When the ATF ruled the Street Sweeper was a prohibited AOW they allowed a grace period for anyone in possession of one to get it registered as a stamped item like any other MG, suppressor, or AOW. This allowed for the already produced items to be "regulated" and stopped the production of any new street sweeper devices for civilian use. There have been a few cases where they redefined a legal machine gun into an illegal machine gun and then confiscated the items. The big ugly question here is that a bump stock is closer to a machine gun than a binary trigger. But neither of them are a machine gun by the strict definition of the law.