right now, the last scheduled gamecube game appears to be Ratatouille on 6/26
the EA press release about the new harry potter doesn't say that the game is in development for gamecube (wii, 360, PS2, PS3, PSP, DS, GBA, PC), and since EB/GS isn't taking pre-orders for a gamecube madden 08 either... i'd assume that EA has abandoned the system...