Hmm, other team-up projects. Inspired, perhaps, by Super Mario and Donkey Kong? Maybe a big platforming game with those two and their friends was considered.
Besides the sci-fi universes (F-Zero, Metroid, Star Fox) and the cartoon/whimsy universes (Donkey Kong, Kirby, Pikmin, Super Mario), I can't think of other Nintendo team-up combinations that have a chance of working out.
Maybe a cross sports game between Wave Race, Excite Bike, and 1080 snowboarding? Advance Wars, Fire Emblem, and Kid Icarus don't fit with any other series.