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I think cryptos have a future as a free market currencies. Fiat could survive alongside cryptos but would not survive if gold and silver make a comeback.

It's hard to imagine a world without some kind of commonly used currency as a measure of value be it precious metal backed or fiat. I'm guessing cryptos will best suit the machine economy, that is, payments between machines through lightning networks. They could have a role, possibly a large one as payment and settlement methods. For long-terms loans they are far too volatile and very likely will be for the foreseeable future.