I'm a bit of an oddball when it comes to my most wanted, but that's alright.
1. Daitoryo
Frankly, I have him as my number one because I would be beyond stoked to see my prediction on him turn out to be right. Secondarily, I actually really enjoy Hanafuda cards, owning a Daitoryo Deck, a Mario deck, and an old non-Nintendo set from likely the early 1910s or so in pristine condition.
2. Elma
This is an extremely hard one to pick, but I adored Xenoblade Chronicles X, and Elma was my favorite of the main cast, no question. Her dual-swords and dual-pistols setup would be awesome to have in Smash, and I think I would pick her up intuitively. It would also practically guarantee that Nintendo still cares about that branch of the series, which would be awesome.
3. Captain Toad
I love this character maybe a little too much. I've supported Toad in Smash since middle school, and he just keeps growing on me. I'm hopeful that the good Captain will be recognized and that I'll get to try him out at long last.
4. Takamaru
Elma, Captain Toad, and Takamaru were all fighting for the second spot, and Takamaru ended up here only barely behind them. I've played The Mysterious Murasame Castle myself, and I loved it. I've collected an insane amount of historical stuff about him online, and his story just fascinates me. He's a Samurai/Ninja apprentice who saves Japan from an onslaught of aliens that go down in history as the Japanese yokai of lore. How cool is that?!
5. Ganon (Beast)
The villain of A Link to the Past, A Link Between Worlds, Breath of the Wild, and the ultimate form of Ganondorf in Ocarina of Time and Twilight Princess. He's a giant boar with a trident and offensive magic that other Zelda characters can only dream of. Fire, lightning, darkness, summoning, and transfiguration are all powers of this dude. His realization in Smash is unlikely, but would be truly awesome.
6. Ridley
God, I love Ridley. As a character he's menacing and cunning, and as an enemy he's a terror to behold, a dragon with a tail that can pierce the hulls of warships and fire that can roast hunters alive. He's so filled with potential, and I would give up an ear for Sakurai to come back to the idea of implementing him.
7. Impa
The Sage of Shadow and protector of Princess Zelda, user of Sheikah martial and magical arts. Unlike Sheik, who specializes in deftness and agility above anything else to protect herself from Ganondorf, I imagine Impa as an adept fighter who would fight tooth and nail to keep what she loves safe. Whether wielding a long dagher, a giant's knife, or a naginata, her skills would be impeccably polished. Further, her use of magical barriers and teleportation would make her difficult to catch off guard.
8. Isabelle
While I'm not expecting her, her charm has definitely won me over. The trusted and beloved assistant of the mayor in New Leaf, she is known for her dedication to her work and her endearing clumbsiness. I imagine her moveset would include a number of aspects of the series that haven't yet been included, namely public works projects, furniture placement, and holiday items.
9. Sukapon
The comedy-robot-turned-battler, I've always had a soft spot for Sukapon. I've played through his game and his cute, pseudo-dancing ranged limb style would be a welcome addition to the cast.
10. Rex and Pyra
I played the hell out of Xenoblade Chronicles 2, and I would love to see a character from the game included, albeit not before Elma. Pyra herself is a lovely character and I have a soft spot for her, so she'd be a make it or break it part of the duo.
Honorable mention: Springman/Ribbon Girl