They're not going to ban e-cigs. Soon, the FDA will classify them, formally, as tobacco products. At that point, they'll impose some regulations. They may be as strict as for cigarettes, or not. The individual states, as well as the feds, will decide what taxes to impose after the tobacco lobbyists tell them how high to tax them. The worst that will happen is that they'll be treated just like cigarettes, including indoor bans and mail order bans. A lot of that has to do with the lawmakers in each individual state.
Some state politicians will get up and grandstand about banning them, but it won't happen. Even if it did, as soon as the FDA classifies them as tobacco products, any law that bans them would be instantly struck down. States cannot ban tobacco products.
As long as they can't ban the sale of batteries, wire, flashlights, food flavorings, PG or VG, there's little to worry about. There are other sources of nicotine if they get stupid about it and try to impose ridiculous taxes on juice.
They can make vaping less convenient and more expensive, but they can't stop it.
Summarized: Will it matter?
The long bit: In all honesty, banning will be ineffective. Up here in Canadialand nic+ juice is banned by Health Canada and there's very little between me and local suppliers. It may involve another step to order, you won't be able to drive down to the market and buy them, but it won't be impossible. The main issue with expecting "prohibition" to work is:
Firstly, tobacco products and smoking in general is still legal and quite prevalent.
Secondly, Ecigs and juice are already on the market, people are already able to get the raw ingredients and hardware through perfectly legal means. People are already building completely custom kits. What will they do? Ban li-on batteries and bits of coiled wire?
The floodgates have already been opened, some of us have been stuck with alternatives that haven't worked for decades. Most vapers I've seen here, like me, are long time smokers who've tried many times to stop, using every trick in the book. Some of us have found vaping to be an almost perfect solution to what is inarguably a health/financial problem. A ban won't stop me, even if forced to attempt imports and seizures at customs, there's no way I'm going back to tobacco.
I bet the only thing that happens is that they tax nicotine liquid, to a point where DIY becomes a LOT cheaper, in my opinion. The government's all about money, so just be prepared for the cost of liquid to possibly rise in the future. I bet it will still be cheaper than smoking though! Even if it's not, I'm NOT touching another cigarette. They smell disgusting to me at this point (3 months in). I quit the same day i got my Kgo starter kit! Fact is, e-cig's work, where as gum and patches just don't (or, didn't...for me).