I re-wrote the second part of my reply. I do not believe there will ever be a case of imaginary digital numbers having more value than something that actually exists. It will always just be a deception involving asymmetric deployment of information:
I guess you could claim the bankers might try to hoist a digital currency scam system upon the serfs, then they would artificially inflate the market cap of the digital numbers that don't exist as more than imagination, and that will somehow surpass the market cap of gold; but at the same time, the central bankers would just buy up and hoard all the gold for themselves. So the gold in reality is more valuable since they value it more than non-existent digital numbers. The whole thing in that case would just be a trick and the gold really would still be more valuable...