Nintendo Announces Wireless GBA Adapter
Thanks to an anonymous reader for pointing to the Yahoo press release announcing Nintendo is using Motorola technology to produce a wireless adapter for the GameBoy Advance. According to the release, "The 2.4GHz radio frequency (RF) chipset enables up to five players to play each other wirelessly, allowing for flexible, mobile game playing", and it "...will be launched in Japan first half of 2004." Motorola is also hosting a picture of the device, showing how it connects to the GBA.
That's totally possible.
It's how the GBA -> GCN link works. GBAs can boot off of the data port, and this lets you have companion programs included on game discs (which is how FF: CC works.)
It's also how multiplayer, single cart games work. Only limiting factor is that the entire program has to be held in ram.
This is how, incidentally, all the new flashrom carts from HK work. No cart-writer needed, just a USB -> GBA cable. Boots a writer program, stick the cart in, and you're done.