Fortunately there are parts of our economy -- like computer DRAM -- that are much bigger than cryptocurrencies.

In order for the bitcoin mining industry to be as big as the DRAM industry each BTC would have to be worth $25,000 each.  And that's only until the next halving, at which point the price has to be $50,000 each.

Proof-of-X for X!=Work is largely off-topic for this thread.  Only POW serves as an origin of scarcity anchored to something physical (computing devices).