If you know how to issue currencies through mutual credit and how to account for them through double-entry accounting, then it is not very difficult to build a cryptocurrency, for which Holochain can provide ample accounting and data integrity.
However, you probably shouldn’t try to do it in the way everyone is used to building cryptocurrencies—in other words, on a global ledger of cryptographic tokens. Determining the status of tokens/coins is what creates the need for global consensus (about the existence/status/validity of the token or coin). However, there are other approaches to making currencies, for example, issuance via mutual credit instead of issuance by fiat.
Unfortunately, this is a hotly contested topic by many who often don’t have a deep understanding of currency design or cryptography, so we’re not going to dwell on the subject in this FAQ. We intend to publish a white paper on the topic soon, as well as launch some currencies built in this way.