I've largely stayed out of this, because it really is a moot point. There is waaaay too much gang influence for a serious challenge to be mounted.
If I have a 10" AR upper and an operational rifle lower, I have "constructive intent" to possess an unregistered SBR. If I have a file-formed 1/4" bar of 1015 steel with a spring, I have an unregistered fully automatic weapon. Period. End of story. Perhaps I just, "want a cool toy without all that cost..."
Perhaps. I have no reason to own an unregistered SBR/FA, unless I intend to do harm. I have shown willingness to risk mandatory Fed time, and total financial dissolution for my "interest". If I'm really dumb, that's really sad. Most unregistered SBR/FA DIYs are not used innocently.
All government agencies have regs on the books criminalizing "intent," because (oh, my gosh!), it might be better to stop some acts before they happen.
https://chicagoganghistory.com/gang/gangster-disciples/