Yeah, an emulation layer for the 68k would have been tits. AmiJoe would have been exactly that, had it been finished.
Anyway, this is essentially how MOS works on classic PPC hardware today. F.e, a lot of demos run much better because of the 68k emulation (faster than any real 68k as I understand it), yet they still have access to the AGA chipset. Pretty cool. Must be the only way to watch Starstruck on classic hardware without stutters. :-)