To clarify one part of this discussion, the ColdFire cannot be made to run all m68k code by trapping unimplemented instructions because it has some instructions which overlap m68k instructions. In order to have decent performance, something like CyberPatcher would have to be run on all loaded m68k code before execution.
Here's a good overview of the differences between m68k and ColdFire:
http://www.microapl.co.uk/Porting/ColdFire/cf_68k_diffs.html
