Some part of the OS will definitly contain PPC-ASM.
I´ll guess some minor parts of exec.library are coded in PPC-ASM. I´ll guess allmost all the code for translating code from 68k to PPC is in assembler too, but that doesn´t matter anyway.
Also, allthough it´s written in c, doesn´t mean it will compile and run on other hardware. It´s impossible to make all code of a OS platform independant, unless you make some sort of a virtual system.
Now, if Hyperion desided to make of x86 version, the biggest job would be to make an 68k->x86 translater similar to the one in OS4.0.
