I'm very pleased to report that it appears we have some success here! 
CC_333 tested the above modifications in an attempt to boot OS 9 on an OS X-only Mac - in this case an iMac G4 - and had some positive news to report:
Hopefully this overcomes the challenge of letting an unsupported Mac see a Mac OS 9 system folder as a valid bootable system. However it's yet to be seen whether this will prove beneficial toward the aim of running OS 9 on newer hardware, or whether it's only a small accomplishment with many larger challenges still to come, although I suspect the latter. My knowledge on this subject is limited and I haven't even begun to investigate where to go from here, but perhaps this will become more of a team effort as others more knowledgeable in the area of system software chip in their theories and findings.
At least, I sure hope so.
Cheers,
~ Mic.
CC_333 tested the above modifications in an attempt to boot OS 9 on an OS X-only Mac - in this case an iMac G4 - and had some positive news to report:
With the ROM modification, OS 9 was able to start up on this machine, albeit without full video acceleration. (UPDATE: Thousands of colours also works correctly.)
Hopefully this overcomes the challenge of letting an unsupported Mac see a Mac OS 9 system folder as a valid bootable system. However it's yet to be seen whether this will prove beneficial toward the aim of running OS 9 on newer hardware, or whether it's only a small accomplishment with many larger challenges still to come, although I suspect the latter. My knowledge on this subject is limited and I haven't even begun to investigate where to go from here, but perhaps this will become more of a team effort as others more knowledgeable in the area of system software chip in their theories and findings.
At least, I sure hope so.
Cheers,
~ Mic.