What I find odd/amusing is how OS4 seems to have been developed "backwards", but I think that's mainly due to one of the earlier HP explanations about trying to implement it all in emulation, then replacing bit by bit with native PPC code.
However, if I had any talent in software development, the highest priority for me would have been to implement the IDE driver and (U)DMA natively :-) How painful it is to use a machine with an IDE disk running in PIO! Ok, so they're not "using" the machines per se, but get rid of the biggest bottlenecks first :-) - this is semi-joking btw -