It goes all the way back to the release of NeXTSTEP 3.1, which included i386 support. And more importantly it never ended.
The Rhapsody DR1/DR2 releases that would shape up to become OS X Server 1.0 were intel based. And the then released source code for Darwin 0.1/Darwin 0.3 although commercially only released on the PowerPC, still compiles and runs on i386 just fine.
I'm sure with the overhaul of the kernel while going from OS X Server 1.0 to OS X 10.0 where the Objective C driver model was dumped for a C++ framework, along with updating the Mach code from 2.5 to 3.0 broke the i386, but it was quickly fixed in the Darwin releases, making the overall chain unbroken from the inside.
It wouldn't surprise me in the lost years of Apple looking for a plan out of the demise of the 68000 that there would have been projects looking again and again at Intel, especially after the Star Trek project.
