I sold my old MAC's to retro MAC fans (clever me).
I you like Amiga classic OS, look on ebay or buy a Minimig (Minimig deserves support IMHO) or maybe go for emulation via your PC, MAC, XBox, PSP, etc...
Natami is showing progress too if it's classic OS with more power that you need.
If OS4 is more your your thing, then hardware is blossoming around us by the day, SAM440, Flex, 460 etc.. and soon(ish) X1000.
Why the hell would you bother developing Amiga OS for old MACS when now is the time of so much new activity on the scene? That would be pure wasted man hours as sure as eggs is eggs. Manpower better spent on OS4 apps for example.