This is an interesting big of news (though still in the RUMOR stage, mind you) from The Magic Box:
Sega and Nintendo of Japan are teaming up to create a dream team RPG for both Dreamcast and GameCube, tentatively called Sega and Nintendo: The Cosmo Cube (Dreamcast version) and Nintendo and Sega: Dream Come True (GameCube version). The two games will feature popular characters from their flagship characters, including Sonic, Nights, Virtua Fighter Kids, and Virtual ON robots (super deformed), a brand new character named Ages from the Sega side. The Nintendo side will include Mario, Donkey Kong, Pokemons (Pikachu and friends), Zelda and an original character named Odnetnin. The Dreamcast version is planned for a 2001 summer release, and the GameCube version is planned for a winter 2001 release. An official announcement will be made in November.
Again, a very strange development, but since it looks like the Sonic Team will be working on the GBA, it would not be a total shock to see this happen.