The first order of business is something I noticed while watching the trailer, which is that Link didn’t say a word during the whole thing. I want to get this out of the way right up front: if a Zelda movie ever gets made, Link must speak. His muteness in the Zelda series is kind of a curious affair, one left over from the 1980’s when the NES made speech in general rather difficult; you’ll notice Mario is the same way. In any case, the fact that you don’t see Link speak has ended up being attributed to Link’s character, which is a problem.
The thing is, Link isn’t supposed to have character. He’s meant to be a direct link from the player to the game; a sort of extension of the player, placing him inside the game universe with some green clothes and a sword. Again, this was much easier back in the 1980’s; these days, with storytelling and presentation at the sort of levels they’ve reached, it’s hard to use a main character without a fleshed-out personality. Video games are the only medium where you can really get away with this, since the interactive element makes up for it; in a movie, it’d be unacceptable.
This in itself, though, is a rather major hurdle for the potential movie; the first major hurdle, anyway. The moviemaker is charged with the role of creating a fully-fleshed-out character (Link) out of one that has been, at best, half-present. In the games, Link is generally a puppet; he does what other characters tell him to do, rarely ever making a decision of his own. Who exactly would Link be? Would he be some sort of pure-hearted fellow, saving the world for the virtue of it? Would that be horribly boring as a main character? My jury is out on this one. All I can say for sure is that, in a movie, Link would need to be much more than he is now.