Thinking of combining the NAS kit with some M2 to SATA adapters. I think running 3-4 traditional HDDs shouldn't saturate the PCI-E 3x1 bandwidth 99% of the time, and it has big upgrade potential for up to 16 drives this way.

One problem - how should I get SATA power? They use both 12V and 5V, but the GPIO only has up to 5V?