Looks like there will be no need for a Wide Boy 64, or more commonly used, Super Gameboy. It was never a known fact that you would be able to play your GB, GBC, or GBA games on your GameCube...until now.

According to the official Nintendo of Europe site, "...you can play all existing Game Boy games on the Game Boy Advance. Also in the pipeline are a four-player adapter, an interface which will enable online playing and a direct link to the NINTENDO GAMECUBE, the successor to the Nintendo64. This connection will allow you to play every Game Boy game (whether for the Game Boy Color or the Game Boy Advance) on the big screen using the NINTENDO GAMECUBE! Furthermore, the Game Boy Advance can be used as a fully-functional controller for those NINTENDO GAMECUBE games which have been specially designed to support this function."

This is an excellent addition. Finally! I almost wanted to get a wide boy. Most figured enough, but I don't think it was ever confirmed that you could do this with your GBA/GC. Big screen GBA love. Gotta dig it.