I actually tried to build something like this (with cables, not stacked) circa 1990. My plan was to implement a snooping protocol in the 16KB of extended memory. All from discrete TTL components (74LSXXX). Surprinsingly, it never worked.
Then I moved on to playing with machines with ~100 FPGAs where I can instantiate as many RISC cores as I want. I'm not sure I'd want to move back to 6502 for parallel programming.
Then I moved on to playing with machines with ~100 FPGAs where I can instantiate as many RISC cores as I want. I'm not sure I'd want to move back to 6502 for parallel programming.