I'm pretty sure that Apple's internal silicon group rolled their own version, as I recall it came back after they decided to switch to ARM and worked perfectly.
Like a lot of Apple projects of the era someone put their heart and soul and a year or more of their life into a project and it got arbitrarily canned - we hired him ....
Apple did so many of these reinvent-the-world projects in the systems area alone that somewhere on Earth-87 they’re running their Hobbit-based phones on NuKernel and the apps are all written in Dylan.
They were really really bad at actually shipping products for a long time. I love all that ATG stuff: SK8, Dylan, all that blue-eyed object oriented optimism. But hundreds of man-years were put into all of that and Copland and Taligent, and they had nothing to show for it. Apple was so dysfunctional under Sculley and Spindler. People say Apple killed Hypercard but really what happened is people worked on it for years but it got bogged down in feature creep and focus switches, and they never get a functional version 3 out the door.
The first true ARM MMU design was Bob Welland's, who had joined Apple after his stint at Commodore (C900, Amiga 500). It doesn't look like traditional MMUs, because it needed to support the Newton OS and shared address spaces.
Like a lot of Apple projects of the era someone put their heart and soul and a year or more of their life into a project and it got arbitrarily canned - we hired him ....