I've been tinkering with this idea myself: build a 4-6 slot "jukebox" multicartridge with an arduino as cartridge switcher (i.e. pad button combinations, such as Start+A+Up/Down to circle through carts) and some logic gates to select the cartridge to play. Got inspired by the old Sega DS-16 demo kiosk, but it would be awesome if it could be used with multiple consoles (and fit right into an arcade cabinet).