You are talking about Maryland, right? Do you think the MGA would only go after the bump fire stocks? They're going to go for everything, and hope that something sticks. If they copy legislation, you don't have to look any further than California.
Did you know that starting Jan 1, in California, they will no longer be able to order ammo through out of state mail order companies and have it sent to their house? They will have to have it sent to an FFL and then do a background check for their ammo.
The famous bullet button is another thing they could adopt from California. There are far too many options they have, to think they'd only be interested in a bump fire stock.
Just one man's opinion.
California is even worse on ammo. CA DOJ is holding up the ammo sales license they were required to roll out the final info on back in July. Shops other than FFL's were supposed to under the new law, be able to apply for an "ammo sales license". The CA DOJ has only now submitted the procedure for public comment although the sales restriction will take effect Jan 1 2018.
If a non FFL sporting goods store has a stock of ammo on Jan 1 2018, they cannot sell it until the CA DOJ starts the ammo seller's license and issues one to them.
A law that the government doesn't follow, should be 100% void.