If a perfect Gameboy flashcart were to exist, it must have the following :
SD or CF card support
Save to card
Menus with subdirectories
True MBC1/2/3/5 emulation
Real Time Clock Support
Rumble Pak Support
The cart should be able to completely hide itself from the Gameboy and game once the game has loaded. This is necessary to counter games that try to detect copiers. The cart should also not be able to interfere with SGB enhancement detection or CGB palettes for DMG games.
Nice things to have would be support for Digimon MMM01 and Kirby's Tilt 'n Tunble MCB7. I do not believe flash ram or eeprom support is necessary for non-Japanese games.
SD or CF card support
Save to card
Menus with subdirectories
True MBC1/2/3/5 emulation
Real Time Clock Support
Rumble Pak Support
The cart should be able to completely hide itself from the Gameboy and game once the game has loaded. This is necessary to counter games that try to detect copiers. The cart should also not be able to interfere with SGB enhancement detection or CGB palettes for DMG games.
Nice things to have would be support for Digimon MMM01 and Kirby's Tilt 'n Tunble MCB7. I do not believe flash ram or eeprom support is necessary for non-Japanese games.