As exciting as it is to design a low power system, it's kind of pointless in the case of a NAS that uses spinning rust as storage media - as the author later writes, the HDD power consumption dwarfs the other system components.

If one uses SSD or M.2 drives, there are some solutions on the market that provide high speed hardware RAID in a separate external enclosure. Coupled with a laptop board they could make for a decent low power system. Not sure how reliable USB or Thunderbolt is compared to internal SATA or PCIe connections though... would be interesting to find out.