I think the issue that prevents anything revolutionary is captured in Storm's post. If they go all the way and make the game only playable with a GC-GBA combo, they reduce their market for the game to people with that setup and annoy people that want to play the game but don't have a GBA and adapter. This is why so far it is only used for relatively unimportant things or in an alternate gameplay mode (MP).
Hybrid Mode
