Well, the majority of people does this sort of el cheapo NAS with an old 2.5" disk lying around. If we get back to the basics (see post #10 and especially #11 from my 2nd link above) we see that random IO with HDDs is crap anyway and that sequential throughput is also limited especially if the disk will be filled to its whole capacity (ZBR -- zone bit recording is responsible for empty HDDs being almost twice as fast as full HDDs)
For this use case Gigabit Ethernet and USB2.0 attached storage is already sufficient, if we've seen how A64 with an UASP connected SSD outperforms A20 with the same SSD connected through SATA when it's about random IO (3rd link above) then it's obvious that 'SATA' is not an own value but it depends on the SATA implementation in question (again: 2nd link above). So regarding el cheapo NAS an OPi PC2 combined with good USB enclosures is already sufficient. Gets even better if Xunlong will make such a NAS Zero with H5 and GBit Ethernet.
Regarding performant NAS attempts in SBC form factor please be aware that there's ESPRESSOBin and maybe other Marvell designs will follow.
Edit: One of the real advantages of SATA regardless of performance is that you have better control over HDD/SSD features (checking drive health with SMART, setting disk sleep parameters, being able to make use of TRIM). This is stuff that does not work automatically with USB but it always depends on the bridge chip used in the enclosure (and that's why I love Xunlong's decision to put 2 of the best available USB-to-SATA bridges on their NAS Expansion board, now only the appropriate H5 board missing )
