OK, cool. I thought early GBA flash carts (1 game at a time) used some type of common multiplexed EEPROM without a memory controller or bank-switching. I was thinking about A 'GBA RAM cart' that would use the GBP and homebrew to load and play ROMS from SD/DVD on the fly. There is already a homebrew ...

how were early on-board memory flash carts setup?
do the early flash carts work with the GameBoy Player? GBI?
are there any early flash cart schematics kicking around?
is there any ROM compatible RAM chips without the need of a memory controller?
do you see where I am going with this?