Are you sure we haven't converged on a good thing? Before Unix (and let's be clear, Windows NT uses basically a Unix process) there were lots of process models

Are you sure we haven't converged on a good thing? Before Unix (and let's be clear, Windows NT uses basically a Unix process) there were lots of process models. VMS was very different, CP/M and MSDOS different than that. My mainframe knowledge is limited, but IBM's VM/CMS and Burroughs' Bxxxx machines were different still. Mach, what's underneath MacOS, is quite different conceptually. All those have fallen by the wayside, because of various inadequacies.