FA's Clearstream Onward studies are still the most relevant info out there regarding the effect of vaping vs smoking on living tissue.
http://www.clearstreamonward.com/the-project-clearstream-onward/. Nothing else even comes close.
Unfortunately for all curious/concerned about vaping diketones, no such flavorings were including in the study (nor in the first round, which was Clearstream). I'd so like to see results for some buttery flavors!
Dr Farsalinos also tested a cross-section of vendor e-liquids for diketones:
https://www.scribd.com/doc/238345295/Dr-Farsalinos-study-on-diacetyl-in-e-liquid. Though he found 3/4 contained diketones, he didn't name names, so that didn't help anyone looking for honest vendors of truly diketone-free products. I personally believe little has changed since then - simply because there's no real penalty for dishonest vendors or flavor manufacturers. One thing we DO know is that FA's flavorings with diketones are identified (and there aren't many that would appeal to vapers...who really wants to vape asparagus forcryinoutloud); their other flavors truly contain none, and their test results are unparalleled.
At least with DIY we can choose for ourselves and know for sure what's in our mixes.