Elaine, this brings us to the subject of AVPs and zero nic liquid. I haven't bought an e cig "system" since '09 when I wasted a bundle on Blu. There I was buying nicotine laden cartridges and the hardware. I can't remember if they offered Zero nic back then since I only used them a couple weeks.
I see no way that the FDA can make a case for regulating the use of flavored PG/VG or the device you vape that non-nicotine mixture in. The FDA has responsibility for drugs and now tobacco products which a 0 nic AVP is neither.
With that in mind, I can only see a couple avenues that can take towards regulation. First, and obviously the preferred option, focus on liquid quality unless it's a system such as NJoy or Blu. The second could take any number of forms that would require pre-filled, proprietary nicquid dispensers.