We speak here of different generations of 68k CPU, like in PC world the different generations are not pin compatible. You can not stick a Core2Duo in a 486 motherboard.
That's not exactly a fair comparison. A Core2Duo won't work in a 486 motherboard, but it will run pretty much all code written for a 486. A ColdFire CPU won't execute all code written for the 680X0 line. Even the trap-based compatibility library doesn't make it 100% compatible, though it's hard to say what percentage of Amiga software would have problems. A relatively simple dynarec (well simple by dynarec standards anyway), could take care of the rest of the incompatibilities, but it's unclear whether the parties involved in these ColdFire projects have the skill, time and resources to make it happen. And of course, once you start talking about emulation you have to ask yourself if you would be better served with a more powerful processor of a different architecture, but if you're asking those kind of questions you probably shouldn't be troubling yourself with accelerators for obsolete computer hardware anyway.
I personally would like to see a ColdFire accelerator and/or ColdFire + FPGA chipset implementation even if all it could run was AROS and recompiled apps (assuming a full 68K port of AROS ever gets off the ground anyway).
