> If I understand correctly, by design PoW gets harder with time, so it becomes ever more expensive to mine BTC. You misunderstood (or possibly were confused w

> If I understand correctly, by design PoW gets harder with time, so it becomes ever more expensive to mine BTC. You misunderstood (or possibly were confused with the ethash "ice age"). PoW difficulty follows daily dollar emission, which is proportional to the product of price and block reward. In Bitcoin there is a large lag (up to 2 weeks) though between changes in the latter, and changes in difficulty. Miners who can't turn a profit will stop mining Bitcoin, causing difficulty to drop. It will always be profitable for the most efficient miners.