Your first assertion here is incredibly wrong. ISA's don't split up as cleanly as your fictional version, a NAS box has to support all the same branch, arithmetic, and memory operations as a "multi-purpose" architecture. The only conceivable things you'd bolt on would be things like NEON accelerators for AES, and there's better ways to do that than mucking about with the ISA.
Do you get folks coming back for a second reply after this charade is made apparent?