There's a lawsuit afoot.
Here's my prediction.
Mr Cox is going to Federal Pound You In The Ass Prison®, and he will remain there.
Most of his customers are as well.
This suit will go nowhere and change nothing.
I wish that it were otherwise, but I was paying attention when these states-rights preemption laws were being passed and listening to what legal scholars were saying about them.
They were symbolic and did nothing to change Federal law. The best you could hope for was that the state law enforcement would not bother you or help the Feds when they came to get you; but it wasn't going to stop the Feds from coming to get you.
I don't think Mr Cox's suit will get any traction because NFA items don't matter to the 500 lb. gorillas of gun rights and the few NFA specific gun "rights" groups seem to have more in common with BATFE than most NFA owners.
I will dance a happy dance if this suit actually gets to the Supreme Court and gets a positive ruling; but I'm not going to hold my breath.