These already exist, in limited form. Check this out:
https://www.fasttech.com/products/0/10005102/1401101-tecs-msk-2000-variable-volt-watt-starter-kit
An e-cigarette, with a flashlight head (510 threaded!) I hope FT starts selling the 510-flashlight head separately!
The weak link, of course, is the nicotine. And the greater threat is not the FDA, but local legislation. They may decide to tax e-liquids "At the same rate" as they tax cigarettes. I've heard mention in the press that "1ml of
juice is about equivalent to a pack of cigarettes" (Ignoring what the nic level is in the juice!!!) Of course this comes from the cigalike companies who would like you to believe that one of their cartos is equivalent to a pack. I believe the state tax in MA is about $3.50 per pack. So a 10 mL bottle of juice would come with a $35 tax.
Some states have tried to include "Any hardware and/or accessories" as part of the tax umbrella. Of course, they're idiots; good luck enforcing that one. But just in case, I've learned how to make an e-cigarette out of an abandoned car, or a flashlight, or the USB port on my PC plus some cat fur, etc.
It's all about the nic. Oops - I mean the money, right?