On the S-100 80386 CPU board there is a special connector “over the top” for memory boards with full 32 bit addressing and 32 bit data width. The S-100 bus serves for accessing base memory and IO mostly since it is limited to 24 bit addressing and 16 bit data width. The S-100 80386 CPU board can work with just bus memory but is limited to 16MB of 16 bit wide memory and is going to be slower than with the special memory board.
Assuming we move forward with a more advanced 68K series processor (68020, 68030, 68040, etc) on the S-100 bus I recommend a similar approach if not the same “over the top” memory boards to make them more economical and provide a useful amount of RAM to more powerful CPUs. I was considering using the PAK68 approach for a 68020 or 68030 CPU socket mezzanine board for the S-100 68K board but in retrospect it would probably be better to design a new board instead.
Thanks and have a nice day!