Eventually the secret sauce will have to be quantum resistance.
But proof of work was a solution to a problem. It's not a perfect solution though because as energy costs rise, and they will, it prices new miners out of the market.
That solution had now become the problem in my view. We need a quantum resistant proof anyway. Without that the house of cards will fall.
POW was a good stopgap solution but I don't think it can remain that way.
energy costs have been decreasing for the entirety of human history if you do not price them in debasing fiat currencies. The progress of human civilization has been a direct result of our ability to more efficiently harness energy from the environment. With technological innovation that will only continue and energy prices will continue to drop.
There is no "house of cards", everything is working as designed and will continue to.
As for quantum computers, that has nothing to do with proof of work that has to do with the encryption algorithms used in bitcoin. If such a thing as a quantum computer is actually possible, and it in someday in the future developed, then we need only change the encryption systems to use quantum resistant algorithms, which already exist and are well documented.
