[abecedarius]

saying that we should hardcode our filesystems into a single machine instruction and let the processor figure it out

I think he was rather saying that the OS could do it: persistent virtual memory as the primary abstraction. In Unix, files and processes are different kinds of things; in KeyKOS there were only processes; RAM was effectively a cache. As Unix directories have links to files, KeyKOS processes could be given capabilities to invoke other processes (passing capabilities and data as arguments). The different security model makes this analogy misleading, but you can see how you could emulate a filesystem.

What assumptions do you mean?