I would love to see another Shadow Link. But I would love to see him have a history, like he was created by one of Link's inner struggles. Or a 'Shadow Link' that is another actual character, like an anti-hero that shows up every once in a while through out the adventure and grows stronger with Link every time he shows up. He could be the cause of some side missions, aside from the traditional temples, that do not have to be completed at a specific time.

As for weapons, the way to defeat him would be different at different battles with him. Defeating him would be a puzzle itself just as we would see in a temple. The key to winning would not be focused on what weapon you got most recently but other means...