I have no doubt you're right; there will be an "informal market". Where there's a demand, there will be a supply.Back when I joined ECF, it was almost entirely to combat the panic mode that was prevalent at the time. It wasn't too long after that I made a wager with a ECF member (used to be a prominent regular) about how much longer we'd be able to get product on the open market. I'm fairly certain the wager was for no later than 2015, as that was determined to be the time, we'd no longer have product available (namely eliquids with multiple flavor options).
At various times since then, I've countered all panic situations on the forum. It helps my ego knowing I was on the right side in those times, as in vaping has gone on without a hitch all the way up to now.
I currently think it is time to panic. At the same time, there's still plenty of reasons to be hopeful, and very good reason to believe a market will persist for adults who want to put eliquid in their devices, and have a multitude of flavor options. Quite likely teens will be in that market as well. Indefinitely. But the fact that DIY currently exists and stockpiling surely exists, means a market will persist, and some are about to get very rich if government tries to prohibit vaping to any degree on the open market.
With that said, ANTZ is pouncing hard enough right now, to bring the open legal market to a screeching halt. They'll fail, for sure over the long term. But they'll succeed enough to not just panic some vapers, but a whole lot of non-vapers who will be convinced that vaping nicotine is deadly harmful. You could die tonight!
Feel free to counter my current take on the situation. I probably wouldn't put up much resistance. But I do think by mid 2020, or for sure by mid 2021, the open legal market will be greatly curtailed (i.e. 95% of what's available now, won't be). Yet because of how much I believe the black market will be popular, I'm not worried.
But personally, I'd rather not buy from "informal" vendors. I'd prefer to know exactly what's in my juice. We're seeing what the "informal" market for MJ extract vendors can do to people right before our eyes, and we know from past experience ~100 years ago that the informal market for alcohol often produced sub-standard or outright hazardous product. Thus I have absolutely no regrets that I spent 2-1/2 years socking away a lifetime's worth of nic base in my freezers, and four years accumulating really nice mechanical squonkers and quality atties that will outlast me.
Furthermore, in another year or two, it will be rather difficult to convince smokers that a switch to vaping would be beneficial to them if they have to buy their vape goods in a back alley somewhere.