I'm not that knowledgable about programming, but I noticed that the genesis expansion port is mostly connected to the cartridge port.
The SMS/Mark III expansion port is a male version of the SMS(usa, Europe, Brazil etc) port.
What I'm thinking is an adaptor could be made that would allow one to connect the FM sound unit, and thus play FM sound games on a Genesis/MD with full sound.
I'm going to register with SMS power and duplicate this post there. Perhaps I'm on to something, perhaps not. But I think it's a cool idea.