The FDA probably has never heard of WTA, and I seriously doubt that they care either, given that it is only a miniscule part of the overall business. There's nothing particularly offensive with it from a regulation standpoint either, as it is still a tobacco extraction, only the process is a little different. These people object to nicotine juice enough. I think that some vapers think that this is some sort of Frankenstein concoction and then project their unreasoned fears on the government as well.
So I went to this site and they are saying that they won't sell it until they "have enough data to support it as a safe and viable addition." This is kind of funny as it's not an addition, they are removing it now as this is already a constituent of tobacco. I think that this is something a lot of people get confused about. What's evil about tobacco is due to burning it and inhaling the fumes. So that's something I've done for several decades and I don't need data to tell me I am far better off.
Shortly after I quit smoking I looked into both Swedish Snus and WTA. My intent wasn't to find which is highest in safety as I knew both were much, much safer than smoking, something that no one would dispute. Now as far as I'm concerned there's already more than enough science supporting Swedish Snus, which we know is a tobacco product that contains nicotine and minor alkaloids along with whatever else and has been shown to be pretty benign. WTA only contains nicotine and minor alkaloids. So by a simple inference we can assume with a high degree of confidence that WTA is at least as safe as Swedish snus.
So I ended up going with WTA mostly because I like to vape instead of using oral tobacco. Snus has removed certain constituents that regular smokeless tobacco contains which is the reason for its much higher safety profile. WTA isn't one of them. I cannot think of a good reason why anyone would be concerned about WTA, and we'd really need long term human studies like they have with Swedish snus to have the same level of confidence.
I can't imagine any need for it though, but of course there will be people that insist on it. We don't have any such studies for vaping regular juice though which is more than just nicotine as we know. All vapers are relying on reasoned judgement to determine that there is some big time harm reduction in vaping versus smoking, and vaping WTA isn't really fundamentally different.
Of course we all need to make up our own minds about whether or not we want to use something like WTA or not, however we need to try to use the same quality of thinking that we used to get turned on to vaping in the first place, and if we do that, and be guided by reason instead of unbased fear, then we are free to judge each product by their own merits, as we need to.