There is no actual evidence as far as I'm aware of. I re-read the post from the chemist, and I agree there is no suggestion there that PG is better or worse than VG. It is a good post with chemically sound advice, as a chemist myself there is nothing there that I disagree with.
Until I actually see someone show some data and offer a chemically coherent reason why PG should be much better than VG (or vice versa), my advice is just pick whichever you prefer for whatever reason. I am inclined to believe that the widely held opinion that PG is much better for long term storage is simply an idea that has been repeated, believed, accepted and further repeated - a fact that now makes it more or less impossible to find any real data if you google the subject. I personally prefer handling PG solutions because I find the viscosity of VG can result in messy transfers.
I doubt there is much difference because nicotine is a lot more prone to oxidative degradation than either PG or VG. Basically the nic will "go off" long before the VG does. PG might have a better shelf life than VG, but that's irrelevant given the the shorter shelf life of the nicotine. Another important point is that VG is probably often given a shelf life based on it's application as a food product, in which case it is likely to be very cautiously estimated using different criteria from those applied to the shelf life of PG. As a man who readily risks an out of date yoghurt (and a chemist who often uses reagents well past their official shelf life) without ill effect, I personally wouldn't pay much attention to the shelf life claims of VG or PG. Really, this is not something to lose sleep over.
My "the nic will go off first" argument is admittedly a very simplified one. It is true that the rates of reactions (like oxidation) vary depending on solvent (like VG and PG), so there could be differences. In this case, I would expect those differences to be small and of little practical consequence, because VG and PG are basically pretty similar in this context. The high viscosity of VG should be beneficial for long term storage, because it slows the rate of diffusion and therefore the rate of reactions.
Another reason why we might predict a solvent to be less suitable for long term storage is the possibility that the products of solvent degradation react with nicotine or even catalyse nicotine degradation. As far as I'm aware, there are no alarm bells with PG or VG; in any case, they degrade into similar cohort byproducts, so it's hard to predict whether one would be better than the other.