As long as there is 0 nic
juice and people who buy it, they couldn't win a case to get PVs outlawed unless they could show they are inherently dangerous. Considering all the medicines that are delivered by PV, that's unlikely.
Were they to make liquid with nicotine illegal, I'd expect many of the current vendors would sell 0 nic only so the unflavored nic juice would be the only problem. If you got your hands on that, it would be "add water and flavor to dilute it to the desired strength."
I'd have no problem paying sales tax on my supplies. I would have a
big problem paying excise tax. The feds have a $1.01 excise tax on cigarettes. Living in New York City, I was paying $4.25 in city & state excise taxes on top of that
and sales tax on that $5.26 (close to another 50 cents.)