This is an old memory, but I thought there was about an ounce of recovered gold on the planet per person, and as we make more people, we tend to find more gold.
This could be totally bollocks, but at an ounce a person, and at US$1500 an ounce there is some 9 trillion in gold out there.
Global GDP is something like $10kper person, (again just ballpark stuff) or some 60 trillion.
So, to switch to gold and to allow there to be enough gold to represent one year of global GDP, gold would need to appreciate by something like 10-fold.
Given that gold has real industrial applications, it would be presumably devastating to those industries.
Presumably folks would return to things like brass for wedding rings, and somehow in the end, because gold supposedly has real value, the world would somehow be better, more stable and so on.
I can't paint the path from here to there on that. It seems gold's value would become arbitrary, based on monetary needs (rationalizing economic output)... just a shiny fiat currency. Where is the magic in gold?