The only way that would be an economic problem is if the fixed-supply currency were the only currency, i.e. the one and only legal tender. That seems very unlik

The only way that would be an economic problem is if the fixed-supply currency were the only currency, i.e. the one and only legal tender. That seems very unlikely to happen. Even if government currencies were to somehow disappear, it would still be trivially easy for anyone to launch a new currency, just by deploying a short script on any smart contract chain. With multiple currencies, we're closer to the competing private currencies advocated by Hayek, who thought they'd bring about a stable economy without need for manual intervention. I'm not competent to judge whether he was right, but it's clear we're not going back to an equivalent of the gold standard.