I think virtualising the 68k would be virtually impossible (if you excus the pun), since the emulated chipset would not have the correct timings with respect to the CPU... That's my guess. You would have to emulate both chipset and CPU... I think... Not sure exaclt how a JIT would work here 
Thought experiment for the day: Which would be fastest (theoretically at least and ignoring the chipset issue).
An x86-JIT'd 68k interpretively emulating a 68k
An x86-JIT'd 68k JIT emulating a 68k
An x86-JIT'd 68k virtualising a 68k