Game Man Advance?
Game Boy PDA? Well, I don't know what you'd call it, but I think Nintendo has a golden opportunity to make a killing in the PDA market. Games on your PDA is not new, but have you seen them? Today's PDA wasn't designed for playing games, so why don't we let a gaming company do it right?
I'm picturing something like Sony's CLIE (the one with the hi-res, swivel screen) that has WLAN; a 320x480 color, backlit screen; 66 MHz ARM processor (or better); Palm 5 O/S. Now, add to that a slot for Game Boy / Game Boy Advance games (and "Game Boy PDA" games that take advantage of the faster processor and expanded memory). The same expansion slot could be used for add-on memory cartridges or other devices (the WLAN support could be implemented like this, but I'd prefer WLAN to be built right in, allowing for multiplayer wireless gaming of course). If they could fit a cell phone in there that would be nice too. The games on today's cell phones look truly pathetic.
Nintendo wouldn't even have to build this themselves-- they could simply license the GBA to other companies to build the Game Boy technology into their products. And with that many more devices out there with little GBA-sized slots, that's bound to spur more cartridge sales.
This might be easier than you'd think-- the existing GBA is an ARM-based system. The same processor that powers Palm devices.