It was speculated and rumored, and now it's confirmed!
Not only is AM2's President, Yu Suzuki, researching GameCube, his teams are also apparently developing for it!!!
In Sega's most recent UK version of its Official Dreamcast Magazine, AM2 was listed among the 2 other known Sega GCN developers. Tendo Box also quotes the magazine as stating all 3 have been at work since last Fall! All rejoice!