If enacted, wouldn't this just "offshore" or offstate" the printing of these parts to other locales ? Then end users would smuggle or ship them into Washington State if desired there ? Seems it's somewhat like marijuana: Legal or quasi legal in like Oregon and Calif., but in outlawed states end users just order through the mail from a dispensary in those states where available.

This seems like a plainly bad idea, though that doesn’t lessen the chances of it becoming law. In practice, it’s silly — building 3D printers side steps it, yes? Can I print nothing when the registry of banned prints is down, as it will very often be as government run software that doesn’t generate revenue. Oh, of course there will be a printing tax to cover the costs passed later. A comic tragedy.

Edit: typo

So what stops someone using a blocked printer to print an unblocked printer to print a gun?

Prusa MKIII. Good luck with that WA. There are enough of these floating around that that cat is firmly out of the bag and they're more than good enough for that kind of work.