If I understand correctly, by design PoW gets harder with time, so it becomes ever more expensive to mine BTC. At some point, it should be economically unfeasible. Now, BTC is rewarded for transaction validation. Does this mean, that at some point in the future, it will be impossibly expensive to validate a new block, hence making it imposible to conduct a BTC transaction between two addresses?
In a bad case scenario, the block reward doesn't keep a large fraction of available hardware online.