There should always be a valid impetus behind the return of any character across any form of entertainment. The three Triforce wielders-Link, Zelda, and Ganondorf-will all return somewhere down the pipeline as Demise's curse foretold at the end of Skyward Sword. But what of the other characters?
Nintendo proved with Majora's Mask that reusing nearly every character from a direct prequel pays off. If the company pursues a similar strategy with any other title in the franchise there is a high probability it will pay off. Even placing a character in a complete different environment works if executed correctly. Nintendo already manifested this with Malon. She appears in Ocarina of Time, Majora's Mask, Oracle of Seasons, Four Swords Adventures, and The Minish Cap while playing a unique role in each installment.
There are moments, however, when inserting a former character seems force. The example I'd like to provide is not one which has been used but rather has significant fan support. In fact the bolstering of this idea has attracted so much attention that an organized campaign is under way to petition for the return of the Twilight Princess-Want Midna Back. I commend the tremendous efforts of this group going so far as to start producing a Mirror of Twilight replica. But for me it doesn't really click. Don't get me wrong-Midna is my favorite franchise companion but her story felt complete after the shattering of the mirror. Even a minor cameo in a future title would ruin the moment.
Enough doom and gloom on my part. Maybe I've outperformed the task in this thread but clarity is something I strive for. One character who certainly wouldn't be out of place in a future Zelda game is Beedle. He's reared his head in The Wind Waker, Phantom Hourglass, Spirit Tracks, and Skyward Sword, never feeling out of place. His humble work ethic and quirky comments place him among my most wanted returns.