anyone know if somthing like this would work with those "console in a joypad" things that sega have released?
Not without some major hacking and reverse engineering. Even then probably not, as the chips on those things are probably under a blob of epoxy to prevent people from doing this. On the FB2, Atari actually took into consideration that folks will want to do this and they very courteously probided a nice little footprint on the board for attaching a cart slot. It should be a very easy job hacking these things.
-S