No because PoS is fundamentally flawed and is a terrible protocol.
I don't understand enough about that. You can also replace PoS with a protocol that has yet to be found.
In 20 years Biotcoin must be worth several million to be as safe as it is today. Or the fees or the transactions must increase significantly. We know where the reward will be in 20 years' time. But we don't know how many transactions there will be then. Or am I making a mistake in my thinking?
Mining does not validate transactions, miners mine blocks to build ontop of the blockchain and the transactions validation is done by every single node (including the nodes that miners are running). Anyways, what's a thermodynamic maintenance?
Perhaps thermodynamic protection would be a better phrase. I don't know. Be that as it may SHA256 forces the use of energy that can hardly be reduced. Correct? I think it is very secure today. I don't know how I could calculate SHA256 with significantly less electrical energy than Bitcoin computing systems do today.
But if there are fewer and fewer rewards, the price only increases by a few percent a year and not much more comes in via transaction fees, then this may change over time. Or am I making a logical mistake?