This might be a niche market that could expand beyond ARs.
AK 80% receivers are already available - no FFL needed:
http://armsofamerica.com/ak4774receiverflatandrails.aspx
And 1911 80% lower - no FFL needed:
http://www.sportsmansguide.com/product/index/stealth-arms-80-1911-lower-receiver?a=1747831
Those are the only others I know of, I wouldn't be surprised if some others start popping up in the near future with all the gun laws passing around the country - of course, be prepared for them to target the 80% lower market soon too. Buy 'em while you still can.