Research is most likely being done as we speak, but it's not being done to our benefit. There's a recent one that vaping increased airway resistance for 10 minutes after inhalation, though there was no (known) comparison to other types of vapour inhalation (like water). Or failed to mention that most any foreign material inhalation will cause problems. No tin foil hat needed. This stuff takes money, lots and lots and lots of money. Even if everyone on this forum donated 10$, it would be a drop in the bucket. Also, there's more to it than just doing some studies on a couple ecigs. It's not like taking a plant, burning it, and seeing what comes out. (raw)Tobacco tends to be the same across the board, it's (more)easily studied.
PG/VG and their effects have been researched as far back as the 40s, when it was found that PG has germicidal properties when inhaled. VG has been around for a long time also, and is used in a ridiculous number of products ranging from medication to lubricant to make up. There's a reason these are being used as opposed to, say, ethylene glycol.
As far as ingredients of flavouring, they tend to use FDA approved flavouring. Not all of these are "safe", and the community is aware of some issues (diacetyl is a no no, for example). The community adjusts itself and life goes on.
That's just the liquid side, then you have feeds and QC. Are you using a clearo, carto, atomizer, rebuildable? Are they using Kanthal and NR wire for the coil, or nichrome, or something else? What's the filler made of? Are the wicks bamboo, silicate, cotton, stainless? Is that bottle of liquid really just pg/vg and nicotine, what type of plastic is it, was it properly sterilized? What are the quality control measures? What about the prefilled carts, the ones most studied and tend to ship from China, land of health and safety standards.
As you can see, research on something that is quite literally evolving monthly and has so many variations is no small feat. By the time they wrap up a paper and publish it, there's something new on the market. Usually new products are improvements on previous hardware, safety has already been addressed and the market (us) have adapted and moved on. The only thing that they can really study is nicotine, pg, and vg, since they are the only common elements. All of them have been researched, over long periods of time, and have been found to be relatively safe for inhalation.