I would prefer MtG stay away from any more crossovers. However, if we're going to be forced to have them, I think one based on the Dune novels would be pretty great. The sandworms would be, surprise, wurms. The Fremen could be soldiers/allies/assassins, the Bene Gesserit could be wizard clerics, the Spacing Guild pilots could be pilots. Legendary creatures could be Paul Atreides (Wizard Warrior Noble?), Lady Jessica (Wizard Cleric Noble?), Duncan Idaho (Warrior Assassin?), etc... Artifacts could be lasguns, shields, daggers; legendary artifacts could be the Gom Jabbar, Ix cloning tank, atom bomb. Maybe make a Spacing Guild ship a vehicle, or a 'thopter a...thopter? Enchantments could be prescience, weirding voice, etc... Legendary land could be spice mine, or the important planets.
This actually seems like it would work surprisingly well.