Well, most of you are wrong.
First: GBC con't controll the settings/the flippings/scrolling (Yes, SMB and SMB3 have diffrent graphics and scrolling),ect.
Second: They're doing it by game. First they did SMBDX, now for GBA, they're doing SMB2 aka Doki Doki Panic. In the near future, about 2002, or late 2001, they might make a SMB3DX for GBA. Which is in thought already for Miyamoto...