I thought up a pretty good idea while playing the other day...
Rather than releasing a sequel, they should've made the game, so that you could store up to 30 songs on it. However, they could then release Donkey Konga e-Reader Cards containing song data, which you scan on the GBA, and send to the GCN using the GCN/GBA Link Cable, a la Animal Crossing, to unlock new songs on it. Then, you could get rid of songs you don't want *cough* Diddy's Ditties/Campfire Medley*cough* and replace them with songs you do like, similar to the plan they have for SMA4. This would actually probably sell well, bring the e-Reader back, and make everyone (or at least everyone with a GBA/e-Reader/GBA/GCN Link Cable) happy.
Come on, you must admit, I did come up with something pretty genius, there.
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What part of the chicken is the McNugget, exactly?