The only problem I see with cryptocurrency (and it's a HUGE problem) is people aren't actually spending it. Right now people are treating it like an investment, or a forex stock. They're buying it and camping on it, waiting for it to go up... when it comes time to spend, they're not using it as a currency - they're selling it for cash and spending that. It's not being used in trade, and for that reason it simply won't ever catch on. That said, it still has many uses of course.. it's just never going to replace the USD. Ever.