Well I am not interested in a 68020 - why cripple a processor on a bus designed for 16 bit max. The over the top memory stuff is crazy. You are not going to find much software to run on the 68020 without more support hardware (need RTC, interrupts and more memory to run Linux). The S100 is just an expensive slow I/O bus for a 68020 - would be better off making an SBC for it than trying to put it on S100.
You can gain a lot of room on the board if you would go to the PLCC version of the 68K - readily available and use the CY7C199 RAM chips which have a smaller foot print. Having choices in master / slave config is more important.
If the direction is 68020 - I withdraw my interest - I already have plans for a 68060 SBC that would be a lot better direction.