While it may be difficult to target e-juice it won't be impossible and will put vendors out of business by making some BS law banning the sale of flavorings and unflavored e-juice at the same time. Regulation could happen. People would find ways around it but still e-juice vendors should take note this is something to be aware of.
I don't see this happening. I don't know how you would control this. All the individual items are FDA approved.
1) The store sells VG/PG in any combo you want in a bottle. This could be sold with any Nic % you want.
2) The store sells Flavoring in a bottle. This could come with Sucralose or without.
3) The store sells Sucralose.
4) The store sell nicotine.
I can't believe you could regulate this. They are already approved substances.
Here is a little analogy. Back when Oleo came out with Margarine, the dairy industry got really upset. They demanded that it could not be yellow. So Oleo, sold you a cube of margarine(butter and margarine came in cubes, not tubs)

, and in the same package was a container of yellow dye. You mixed the two together and Yellow Margarine.
If the FDA, does come up with something, and we can't beat them off, I see these scenarios.
I go into a ecig store or order online. I get a 14 ml 70/30 p/v 12mg nic in a bottle. Comes in a 15ml bottle. I get the recommended little bottle of flavoring/Sucralose for in the appropriate size to flavor 14ml of juice. I go home, squeeze the small bottle into large bottle, let it steep for whatever the recommended time is, and then vape.
I go into a ecig store or order online. I get a 13 ml 70/30 p/v in a bottle. Comes in a 15ml bottle. I get the recommended little bottle of flavoring/Sucralose for in the appropriate size to flavor 13ml of juice. I get another recommeded little bottle of nic, which would nic the 13/14ml of flavored juice to 12mg nic. I go home, squeeze the small bottles into large bottle, shake and let it steep for whatever the recommended time is, and then vape.
I think any regs may affect B&Ms more than online vendors. So this scenario may have to happen.
B&M divides the store into different shops. You know like those little stores that have several little shops in them.
One store sells all the vape hardware. Second shop sells VG/PG anyway you want it. Depending on the rules that come out, this second shop could be just ejuice. Or this shop just sells any percent mix of VG/PG or just a couple of percentage, maybe 50/50, 80/20, 70/30, 30/70, 20/80 in various size bottles. They sell nic in various size bottles. They sell flavoring in various sizes bottles. They sell Sucrelose in various size bottles. All the smaller bottle amounts correspond with the amount of raw juice you buy. Or you may need a 3 shop selling some of products.
Would this be a headache for shops and online vendors, yes. Is it workable, yes. Can the FDA make regulations to govern all the different scenarios, I and others could come up with, I don't think so. There are too many variables on how to sell products all ready approved by the FDA.
Just a thought.
Greg W.