Toon Sheik just doesn't make sense, Tetra would have made it instead. A Young N64 Zelda with a new Young Sheik would have made better sense if you ask me. So yeah, YOUNG ZELDA FOR THE NEXT SMASH!
Other suggestions for Smash 4:
Megaman (classic)
Cloud Strife (this would allow Nintendo to add elements from SMRPG as well)
Bomberman
Dixie Kong (they better give her a real voice instead of monkey screams)
King K. Rool (with Gangplank Galleon as his stage)
Eliwood (FE6 version, if Roy is gonna make it, too)
Ninten (from the first Mother)
Pokémon Trainer ♀ (Pokémon Fire/Leaf, with Bulbasaur, Charmeleon and Blastoise)
Brendan (Pokémon RSE, with Mudkip, Grovyle and Blaziken)
May (Pokémon RSE, with Treecko, Combusken and Swampert)
Meowth (Final Smash: Meowth's Party)
Paper Mario (Final Smash: Mega Mario)
Impa (N64, why want a standalone Sheik when you can have HER?)
Young Zelda (Young Link needs a partner, not only older Link)
Wart (Super Mario USA)
Costumes:
Peach: Sports, Strikers, Ponytail
Mario: Classic 1985, Strikers, Dr. Mario
Pokémon Trainer ♂: Game Boy, Ash Ketchum
Sonic: Classic 1991
Brendan: Emerald
May: Emerald
Young Link: Toon Link (they should have made that from the start)
Link: N64 or TP
Ganondorf: N64 or TP (it also applies to his Final Smash)
Stages:
Airship/Comet Observatory (Super Mario Galaxy)
Bowser's Castle (Super Mario RPG)
Peach Circuit (Mario Kart 64)
Rainbow Road 64 (Mario Kart 64/F-Zero X)
Famicom/NES (Similar to Wario Ware, but you play through many 8-bit classics)
Yoshi's Safari (Similar to the racing stages)
Flipside Tower (Super Paper Mario)
Bowser's Battlefield (Paper Mario)
Glitzville (Paper Mario RPG)
Mushroom Castle (Mario & Luigi RPG 2)
Yoshi Topsy Turvy (a tilting stage)
Ganon's Tower (Ocarina of Time, the tower collapses as you fight)
Gangplank Galleon (it navigates between DK Island and Crocodile Isle)
Subcon (Super Mario USA, it should also use sounds from Doki Doki Panic)
Who knows, maybe Nintendo is going to move to Bluray for the next system in a few years.