Building a basic mod is easy. Batteries are never going to be outlawed. You can make a tank out of stuff from Home Depot. People who are re-wicking already buy their stuff from fabric shops and whatnot, not just from vape stores.
PG and VG and food flavoring are widely used outside of vaping.
What you should worry about is nicotine. I expect big tobacco to push the legislature to make strict requirements on who can sell nicotine (in the name of safety, of course) so that essentially nobody but them can meet the regulations. At that point, they more or less own the vaping market, and probably the only thing they'll sell are low end cigalike models which you can't refill.
The other necessary items they can't really control, but nicotine, they probably can, and probably will. And it won't have anything to do with whether we've been vaping in public, it's just big money companies trying to corner the market.