I am considering to make the same move. Provided that someon already has a Mac Mini G4, besides MorphOS what else is needed to make it work as an Amiga PPC? My intention is to be able to run AmigaOS 4.1, but I'd also love to play and use classic Amiga software. Is the late even possible?
MorphOS and Amiga OS 4.1 have nothing to do with each other, other than being Amiga like next gen OS's that both run on PPC machines. MOS will run on the old PPC Mac's, Amiga OS 4.x will not (officially, anyways). If you wanted to run both I guess you could track down a Peg or something.
MOS supports a fair bit of legacy 68k software out of the box, but for a good chunk of it, like games, you will likely need to use an emulator. OS4 is the same in this regard, and the process is sort of hit or miss, IMO. Fact is neither the Mac's with MOS, or the SAM/A1/1000x/etc have the original Amiga custom chips on them, so if programs are looking to bang hardware directly, emulation is usually the only solution.
You'd be sorely disappointed in either solution if it was your intent to
only run Amiga legacy apps/games, since you can emulate old HW on a commodity PC for free really via UAE.