Volatility is ameliorated by stablecoins pegged to fiat currencies. Furthermore, the long-term goal is to not need an "interface to the real world", because you will be paid in crypto and you will pay for things in crypto. Even then, who exactly do you mean when you say "the people providing the interface"? I don't need a middle-man to agree to exchange crypto for fiat with someone. You can use one, sure, but it's not required.