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.