Vaping will die, not in 20 years, but way before that.
The reason is simple.
As of right now, there is a wide variety of freely available devices, where all vapers can choose what suits them and prices, depending on whether you go for DIY or not, vary from almost equal to down to 1/50 the price of smoking.
Upcoming regulations and bans on specific things will soon limit available devices to disposable minis and lift prices above the price of smoking.
Given the fact less than 3% of vapers want to actually quit consuming nicotine and don't find those minis sufficient in the long run and given the fact that out of those who do want to quit completely less than 3% actually manage to quit through these minis, it's predictable, 97% of all those who try vaping in the future will fall back to smoking in a short time.
In the end that's about the same success rate patches and gums have, so vaping will become yet another useless quitting aid alongside patches and gums.
By the time courts all over the world could (at least in civilized countries) overthrow the completely senseless regulations that instead of increasing public health actually push for more smokers, the e-cig market will be so completely destroyed, there won't be any kind of recovery.
Personally I don't really care, I've got supplies stockpiled up to the end of my life expectancy, but I find it a real pitty, the younger generation won't have this option.