They're letting banks continue with blockchain and distributed ledger tech. It frees them to use securities or stable coins (cryptocurrency) for funds transfers, payments, etc. Basically saying no matter how the SEC goes, XRP can be used.
The letter makes this clear, noting that, as financial intermediaries, banks face competition to move funds faster. In the OCC's eyes, INVNs, such as blockchains and other distributed ledger technologies, are a way of efficiently and speedily moving funds.
Moreover, the letter states that banks may issue stablecoins as they might debit cards or checks, and exchange them for fiat. The OCC makes it all sound hunky-dory: "Banks have long used cashiers’ checks, travelers’ checks, and other bearer instruments as a means of facilitating cashless payments."