It's the cost of regulating those liquids that we need to worry about. As I read the regs. every ingredient of every flavor a vendor makes needs to be certified at $1,500.00/ingredient. Doesn't matter if the already FDA approved PG was approved for the last flavor, it needs to be approved again for the next flavor.
Nah... both PG and VG are GRAS ('generally recognized as safe') category, so they can be used in anything. It's the nic and the flavors they are going to scrutinize. We know they don't mind pg or vg because these are currently used in asthma inhalers... which have the intention of hitting the lungs.
We technically only have 2 things to be concerned about. There's no way to make nicotine illegal, smoking is legal.
So, we worry about TAXES on nicotine, because cigs are taxed... but there's exceptions already, cigars and pipe tobacco are not taxed like cigarettes.
And whether ONLINE sales is legal (you can't buy cigs online because they bypass state taxes). You can't legally buy cigs online, even if you can buy RYO ingredients online (tobacco and filters).