There's M.2 cards with PCIe to SATA bridges, which are great for a high-capacity low-speed NAS setups, especially with mechanical hard drives. Be sure to research the chipset before buying one, as some are notorious for poor driver support.

If this is a practical application, I would recommend sticking with ARM for this generation, as RISC-V is still in early development. In a year or two we should start getting more standardized RISC-V processor implementations, with broader support.