Serious question. Just how many people are running "unregistered SBRs" (depending on how you choose to define that) these days with all the "pistol" AR-15s available? I'd suggest more is happening than you think, and that's a good thing. There's nothing inherently more dangerous from a ballistics point of view about a 10' AR vs a 16" AR.
Serious answer, the people who choose to do so are probably looking over their shoulder for an item they buried in their backyard and never take to the range, that can‘t really be defined as open defiance now can it.
Serious question for you. What do you think would happen if you had an illegal SBR rally at The Alamo? Promote it via different media platforms and have an open display of defiance of federal gun law. You think you would achieve any desired results? You think you would go unscathed?