Well, I agree with the most part, I mean, we've definitely seen a lot from Zelda, but it's been about the same each time, when referring to the game's storyline.
However, looking at the environments, the play control, and everything in that aspect, we've actually had large variations. There's been Volcano areas, island galores, Young Link, old Link, alternate universes, Link on a horse, Link as a wolf, the stealth parts in the Four Swords Adventures, great four player game play, if you had four GBA's. Now, I'm even having trouble seeing what sort of environment they could put Link into without crossing into something they've done.
However, like other people have said, the scenario can be changed drastically. Time and time again, we've scene an unknown nobody, our Link, rise, gain the materials, and then defeat a great enemy, usually Ganon. What if we put a very, very young Link on the run. Ganondorf reincarnated, knows the legend, and seeks out any lad named Link, and he finds him, and sends minion after minion to get him. I don't know, that's just a quick brainstorm, but really, anything to change the formula is great, as the environment is already pretty dynamic.