I think the way the NEO 4 patched the bios were the best solution as it instead of conflicting bits by injection of data on the pins, it does actually decode addresses and patch bigger areas (it's patch is very big, nearly 40kbytes)
Unfortunatelly that makes the chip very limited on which models it can handle as it's heavily hard wired to an specific bios version ... Sony could mess it up just by inverting the order of the modules in the rom filesystem or by crunching them ....
The worst problem on neo4 were the way it unlocked the drive ... It used the SCEX signal ... Origa brothers still rocks !
Kudos to messiah team for the dynamic rom version detection system and "non address bus" patching...
SCPH-10000_GH-001 SCPH-15000_GH-003 SCPH-18000_GH-008 SCPH-30001_GH-005 SCPH-30000_GH-016(V4) SCPH-30001_GH-010(V4)
2xSCPH-10190, 2xSCPH-10350, 2xSCPH-10280
"**** j0 hackers!"
-Sjeep (As seen on TOXIC OS ELF...)