> you would probably need a Gekko->G4 JIT to have GC emulation inside MorphOS.
> Lots of work.

Yes, and on top of that, complete emulation (no matter if static or dynamically recompiled) wouldn't make sense on our comparatively slow hardware.
Dreamcast270mhz's idea which started this thread was that CPU emulation of any kind wouldn't be required when host CPU and guest CPU have sufficiently similar ISA, which I think should be the case for G4/G5 and Gekko except for the SIMD unit.