There was a big change between Rhapsody & OS X. The mach part was upgraded from 2.5 to 3.0 and the BSD part was rapidly being update. The other addition was t

There was a big change between Rhapsody & OS X. The mach part was upgraded from 2.5 to 3.0 and the BSD part was rapidly being update. The other addition was the new driver abstraction library as NeXTSTEP/OPENSTEP on i386 used Objective C, while OS X uses C++. I don't think the code ever really sat that dormant, as they were working on 88000 based machines for the NeXTRISC before that was canceled, and sold off to Cannon who eventually shipped a dual PowerPC 601 machine based on the NeXT design that at the time was to include dual 88010's. There clearly had been some work on PowerPC back when it was first announced as some early code made mention of a MC98601 aka the first gen PowerPC.