Why does everyone think the game would have to pause while one person went through menus? PSO had menus, and it certainly didn't stop and wait whenever someone looked for a spell they don't use often. Small floating menus near the characters, with type icons for easy ID (Ice, Fire, et cetera) that you could crawl with the C-Stick while still running around with the Control Stick. You wouldn't even have to look away from the screen to menu crawl like you do using a GBA.
I mean, if the game works in Single Player mode with just the GCN controller, why can't it work in multiplayer? How does it handle it, DOES it stop the game and stupidly throw up a full-screen menu?
I don't think the GBA functionality should be removed, but I think it should be an option, not a requirement. Purists can play with the GBAs, but there are too many alternate solutions to effectively handle what benefits using a GBA has to require the use of one. No, it may not work with people who have four inch TVs. Those are the people that would need the GBA functionality. Those of us with more reasonably-sized screens should be able to make out four floating text menus with little issue, while still being able to see the action behind and around it. (Semitransparency of the menu background would help a lot, too.)