Well, it needs more than just to replace the CPU. If I would go with a full 68000 I will have a 16 bit databus. Then I would need a second Eprom* and the 16-to-8 bit buffer doesn't make sense anymore. Thus all in all it entails a slew of changes ending in completely reworking the PCB layout. I like the idea though but not without help. But eh you could get off from your couch and participate.
Simon
[Edit] * And a 16 bit width RAM. Probably no 30pin SIMM but 72pin SIMM[Edit]