I agree in that I think all juice manufacturers should list all the ingredients they put into their e-juice, as well as concentrations of each (maybe in percentage form.) Everything we consume in the USA has a list of ingredients, from cookies to vitamins. Why should e-juice be any different? And I am including flavorings in that. Why shouldn't we know the chemicals that give us flavor in our juice? It would be better for the consumer, and it would show the FDA that e-juice manufacturers have nothing to hide. Open and full disclosure, I say. If this stuff is as safe as everyone maintains, then say what's in it and put your money where your mouth is.
As for diacetyl specifically, I am only just now starting to learn about it, so PLEASE don't flame me too hard if what I say next is somewhat naive, but if it's such a controversial substance, and if it's causing people stress over its safety as an inhaled substance, why does it even need to be used at all? What's the upside to continuing to incorporate it into e-juice formulas? It seems to me that keeping it in despite the general public's concerns is not much different from big tobacco tossing unsafe additives into cigarettes to "improve" them, despite knowing that they were unsafe.
Juice makers need to be above that, and dropping diacetyl altogether would be a good move on their part, or so it seems to me.