This topic came up in the last forum and we concluded the 68060 was noyt 100% hardware compatible with the 68040 so the OS would have had to be changed to even get a Mac to boot.
The reason an 060 accelerator was designed but never shipped is because of the above plus the fact that it could not compete in speed with the 601 upgrades being planned/sold.
G3's being dirt cheap now has nothing to do with how fast you can get a 68K to run with upgrades. You do see people blowing $100+ just to get an 030/50 for an SE/30 and $100's more to get 256 greyscale on the same machine.
The reason an 060 accelerator was designed but never shipped is because of the above plus the fact that it could not compete in speed with the 601 upgrades being planned/sold.
G3's being dirt cheap now has nothing to do with how fast you can get a 68K to run with upgrades. You do see people blowing $100+ just to get an 030/50 for an SE/30 and $100's more to get 256 greyscale on the same machine.