I would love to see another form of Shadow Link, but I would love for him to have a History with Link. As in, Shadow Link was created by some horror in Link's past, or by an inner struggle within Link.
Or I would love to see a Dark Link or an anti-hero. Kinda like a mini villan in the adventure. Someone who pops up at different times during the adventure to confront Link. He (Dark Link) would grow stronger with Link and have all of the same items as Link, making him much more difficult to defeat.
Well thats all I have right now. Tell me what you think!