To be honest, I'm curious as to the profit margins involved in selling ejuice, and wether or not they support a mid sized business at all. It's entirely possible that there is a diminishing return on investment and infrastructure (basically more hands mixing and shipping) than is worthwhile to support. So many of the most popular juice makers are constantly out of stock or only open for moments at a time that one would think that somebody out there would take it seriously enough to make a professional run at a full blown business. Hell, witha product like bobas combined with chemical addiction, I'm surprised investors aren't lining up to buy these small companies and generate a manufacturing line based on two or three recipes from each.
My opinion is that what you describe will happen. I assume that big tobacco is waiting for the dust to settle regarding FDA and tax regulations. I suspect that every major tobacco company has a small team investigating ecigs, doing market research and considering their own formulations (and budgeting a few bucks to buy the better ones already established).
I expect that the business model we see now will be gone within the next few years. Just like their were several hundred automobile companies when the car was first introduced and now a winnowed down to far fewer, we'll see the same with ecigs. If what seems like the inevitable happens, the small operations will be crushed by rising capital costs, regulations and compliance:
1. Regulations that either require strict age verification or eliminate internet sales altogether. $
2. Medical safety testing and compliance. This would require staffing with serious medical/pharmaceutical professionals. $$$$
3. Tax collection and all the associated tracking and documentation. $$
It's apparent that most favorite juice vendors are struggling with cash flow, leverage and economies of scale. If they don't have the resources to fund sizable inventory and keep their pipeline filled or (seriously fund a serious web site effort), the added burden of the above factors will crush them and big business will step in. (I'm not criticizing anyone. It's simply a matter of cash flow; not talent, intentions or operational skills.)
The downside is higher cost and probably fewer choices for us consumers. But to be honest, I think that there are maybe 100 really good/great juices out there and a probably a few thousand ho-hum or downright crappy ones.
The upside is that perhaps you'll get your juice at the corner store, in stock, with a 2 minute wait at the checkout line instead of wasting hours stalking a web site like an idiot (like I have been). Further upside, while many seem to disavow the risk, the potential for medical harm would be greatly reduced. (Do you KNOW what's in your juice? Do you feel completely safe vaping something formulated by a guy whose only credentials are passing high school biology [maybe].)
I think the days of the small, unregulated, internet-based juice vendor are numbered. In the long run, we may be better off, although regulation generally means over-regulation and that will cost us in money and choices. Most of the little guys or the bigger ones with low cost but ho-hum flavors will fade away. Our heros, like AVE and a few others, have a good chance of a nice retirement package.