Single Status Update
I own a GBA and you know, I think that Nintendo really dropped the ball on it. They could improve their next incarnation of the Game Boy by doing this :
4 primary buttons, a, b, x, y. Just like the good ol' SNES.
4 triggers, R1, R2, L1, L2. Dur.
2 middle buttons, under start and select, because you know, games need lots of buttons!
2 speakers instead of 1
Backlit screen (like on the SP or whatever)
Larger carts. They're pretty small, if they were bigger in size, they'd be not only harder to lose, but could hold more.
Wireless link-up. How would this work, you ask? Well, you flip a little switch on the wireless box in the same area as a person with a wireless connector and the same cart you have. Now, what if you leave it on and start to play a game, the same game somebody else has? Well, if you were the one that had your GB on first, it would say "Wireless connection detected, prompt for connection?" and then you could say "Yes" or "No". If THEY were the first and they prompt to connect to you, you can of course say "Yes" or "No".
Headphone jack (I know the GBA has one)
Adapter to plug your Super Mega Ultra GB into your portable CD player (maybe even DVD player!)
Backwards compatible with old GB games (like the GBA)
MAYBE an adapter to plug your GB into your computer to upload saved games to your game, activate cheats / unlock content, save your savegames to your PC, and maybe use it to play games on your GB with other people over the internet!!1
Use 4 batteries for extended play, but only 2 required for it to run.
MAYBE use little "flashcards" that can be used to swap stuff without a link-up, you just save the stuff to the flashcard, the person you're swapping with takes it and does whatever. Of course, they'd be re-writeable.
A lid that can be closed to cover the screen.
So, yeah, if Nintendo did all that, I think that it'd be the best GB EVAR
Well, let's see.
Basically, we're looking at a Playstation controller with a screen and wireless capabilities. So, an N-Gage. Heh.
Just a note - size is not at all a limitation on the storage in GBA carts. They're about four times the size of a Sony memory stick, and you can get 2GB memory sticks. ($119.00) The very largest GBA games are (correct me if I'm wrong on this) 16MB.