Maybe I'm dense, but I took it they found some good thick ejuice that they would like to try to replicate using DIY.
If so then VG is what makes juice thick, but it needs to be thinned some so it won't clog your addy. It makes more vapor, but deceases the flavor so you would need to use a higher percentage of flavor if you really like flavoring to come through.
IF VK's is really thick I suspect they started out with nic based in VG, added flavor (does thin some) and another thinner so it won't clog atty's. I haven't made a thick juice yet, but plan on making some that way which is what brought me to this thread.