Why fram instead of eeprom
This sort of thing? https://www.reddit.com/r/Gameboy/comments/3ho3aw/til_that_you_can_replace_the_volatile_sram_in_a/

The trick there is that the FRAM part was seemingly designed as a drop-in replacement with an almost identical pinout to the SRAM chip, and seemingly identical power and timing requirements. EEPROM is usually slower to write, and Flash can only be block-erased.