Empirical evidence won't hold up.
If a government agency decides these are "nicotine delivery devices," the government will regulate them as medical products, requiring the same years of study and expenditure of millions of dollars that it took to get patches, gum, lozenges and inhalers on the market.
E-smoking won't happen if that's the way the flipped coin lands.
Health is not the concern. We all keep arguing they're safer. But there are no studies to prove they're safer than FDA-approved NRT products. In fact, there are no long-term studies proving they're safe at all. We certainly hope so, but hope isn't proof. No one has ever inhaled propylene glycol vapors multiple times each day for years. That's what we're doing, assuming it's safer than inhaling cigarette smoke. While that probably is true, absolute knowledge of safety will be elusive for some time to come. The governments of many countries might ere on the side of "don't sell it before its safety is proven."
If that happens, we're looking at these products being banned.