I think I read it.
I didn’t see in the new law where an 80%, or a block of aluminum as Ren points out, was defined as a firearm receiver. Or even firearm part.
And still haven’t seen the word possess in the new law.
But more importantly, where is an 80% defined as a firearm part?
Anything about firearms parts, other than firearms receivers, refers to may be readily assembled.
It doesn’t refer to readily manufactured, which an 80% would need to be.
You can’t readily assemble an 80% lower.
It does look like you need to Serialize and register it before you begin to manufacture it.
The more I read it the cloudier it gets.
By my reading, unregistered uppers are more suspect than 80% lowers as uppers are un-serialized, un-registered firearm receivers which can be used to readily assemble a firearm.
P.S. Guess I gotta go back and watch Schoolhouse Rock again. 
Conjunction junction, what’s your function.....
They avoided specific wording, because someone in the Legislature finally figured out that the people are smarter than they give us credit for.
If they say "80% receivers are banned," we'll be buying 75% blanks. If they say "possession" is illegal, and there is no accountability for whoever buys these things and then resells them, they'll never be able to find them unless one is found at a crime scene or discovered in a search. So, they banned the USE of these products (gun parts) that can be assembled as a firearm. Use includes manufacturing, buying (purchasing) or receiving (obtaining) one.
The intent is to make these parts illegal in Hawaii -- except for the ones you serialized and registered like normal firearms. If they allow that (which I think they are), then possession of SERIALIZED & REGISTERED blanks is still legal. If the cost is less for these 80% lowers/frames than a milled and FFL-controlled receiver/frame, I can see FFLs doing transfers for 80% receiver parts -- where they make sure you have a permit, and the part is recorded as a "receiver blank" when registering with HPD. Therefore, it would be logical that they aren't banning 80% lowers -- only the ones that are sold without serial numbers and unregistered.
If you obtain it, then give or sell it to someone else, you're still guilty without having to still be in possession. The person you gave/sold it to is still guilty, since they obtained it from you -- possession not withstanding.
You're trying to dissect the verbiage to argue some sort of loophole exists. They made the wording ambiguous and "loose" enough so they can shoehorn in a case involving a receiver blank no matter what part you actually played in it's existence in Hawaii.
The definitions should have been added to the statute in the glossary, but that would just create the loopholes you are looking for. That's why interpretation is left up to the prosecutor -- who refuses to provide the people who pay their salaries and operations budgets the courtesy of providing their interpretations of ambiguous laws.