If what this guy is describing is just taking the lower receiver, or stripped lower, as FOX shows in the article, and substitutes all the other parts (something the AR-pattern allows), then this may be doable, but the phrasing is disingenuous.
But if so, I can see why the ATF would be having kittens, since that's also the serialized part that their own regs considers the "firearm".
Since the lower receiver is the only part that is controlled as a firearm, it could — could — be a way to build an AR without ATF paperwork. It wouldn’t even be that cheap, since these high-quality Airsofts are $200+
The question I have is, “is this even illegal if you are just building a semi-auto for your own use?”
Now, it could put Airsoft and the retailers in jeopardy, since they may be selling an 80%+ lower without appropriate FFL licensing and background checks. However, would it be illegal for an end user to own one or convert it for private use? Not talking about an NFA weapon or a felon owning the gun.