Are there any old 8 bit computer designs,that could be upgraded to modern specs that one could wish for?
32Kb static ram is cheap as dirt. With a write protect switch, EEPROM works great a ROM.CPLD's or FPGA modules
to replace IO chips.

I've seen re-created C= 64s with a single 64K SRAM (with a fair reduction in pcb size too), I have bought modern ROM replacements that use far less power, and I believe there are now replacements for all the chips in the 64. Was that the kind of thing you were thinking of?
In Amiga-land there is a continous quest for coming up with replacement chips but there are still a few missing for a complete build (though pcbs and alternative form-factors exists).