Time to join the bandwagon (Most of this comes from my signature lol, but I'm likely to keep swapping characters in and out between honourable mentions)
1: Isaac (Golden Sun) - Still one of my most wanted characters, even after his AT revelation almost a year ago. Although I didn't play Golden Sun in my childhood, it was Isaac's appearance in Brawl that got me interested in Golden Sun in the first place. His Assist Trophy had a fun ability that could've been translated to a playable moveset, and then further expanded upon with all the other Psynergy spells he has access to - Earthquakes, Vines and plant manipulation, and powerful Summons. Golden Sun is an underrated classic in Nintendo's library that deserves a second shot in the new generation - be it a full on remake or Isaac finally joining Smash as a playable fighter. I'll still wait patiently for that day.
2: Phoenix Wright (Ace Attorney) - I absolutely adore the Ace Attorney games - the crazy courtroom antics, the storywriting and the fun characters that always show up in each game. Phoenix would be an amazing if not wacky fit with the craziness of Smash Bros, and if anyone doubts his potential for a fighter, Ultimate Marvel Vs Capcom 3 perfectly represented him in a fighting game environment. To this day he's still one of my mains alongside Dante and Strider Hiryu. I would absolutely freak out if he came to Smash Bros one day.
3: Rex and Pyra (Xenoblade) - These two deserve a second shot at an invite to Ultimate. As a fan of Xenoblade, Rex and Pyra definitely have a fun dynamic that would be a lot of fun to see in Ultimate and Xenoblade is worthy of having a second character at this point (or even a third in Elma too).
4: Ryu Hayabusa (Ninja Gaiden) - A character I've come to want to see in Ultimate after hearing of the rumours and I think he's a good fit for sure. Brings a bunch of cool Ninjutsu abilities and is one of the last classic characters of the NES era. I've only played the original NES Ninja Gaiden and a little bit of Dead or Alive in the past, but Hayabusa is a worthy fighter for Ultimate.
5: Byleth (Fire Emblem) - I know they're another Fire Emblem character, but honestly after how much fun Three Houses has been so far, I'm definitely okay with adding Byleth to Smash. A whipsword and a wealth of other cool weapons at their disposal (Lances, Bows, Axes, Magic, Gauntlets) and the ability to rewind time sound like perfect ingredients for a newcomer if you ask me. I honestly would prefer Byleth over Edelgard, but would still like to see the House Leaders get a bit of a shout-out too, either as part of a Gambit Final Smash or something else.
6: Akira Howard (Astral Chain) - Just like Rex and Pyra, Akira would be a fun new dynamic to see in Ultimate, a police officer who fights with a baton that can turn into a giant sword or energy gun and fighting alongside a Legion that deals powerful attacks in tandem. Astral Chain is definitely worth including as one of Nintendo's newest IPs in the new Switch generation of Nintendo, and we get some more Platinum Games goodness too.
7: Dante (Devil May Cry) - Another one of my favourite Capcom characters. SSStylish and a badass fighter who would bring plenty of cool flair to his attacks. Not to mention we'll get some of the finest songs in the Capcom sound archives too, "
Devils Never Cry" and most importantly "
Devil Trigger". Just like Phoenix, Dante was one of my old mains back in UMVC3 so it'd be fun to have part of the team fight again in Smash Bros.
8: Doomguy (Doom) - A character that slowly grew on me after I beat DOOM 2016 and realised that, even if he were toned down to fit the age rating standards, Doomguy would be a perfect fit for Smash Bros. Powerful guns, brutal fighting style and the great communicator, CHAINSAW. Yep, Doomguy is my go to pick for a classic First Person Shooter chracter.
9: Takamaru (The Mysterious Murasame Castle) - Another classic Assist Trophy character who deserves a second shot and reboot game to get more people interested in him. We don't have any classic Samurai archetype characters so far and Takamaru would definitely break the mould for regular swordfighters thanks to being more inspired by Japanese swordfighting skills and weaponry. My second most wanted Assist Trophy promotion.
10: Kazuma Kiryu (Yakuza) - After starting up Yakuza 0 properly over the Mid-sem break, I've come to realise that Kiryu or Majima would be an excellent fit for Smash Bros since the Yakuza series is now getting more popularity and attention. There's so much potential for him to be a fun fighter with either multiple fighting stances as seen in 0 or the Heat System to pull off stronger and stylish moves, that you have to think that if he showed up in Smash Bros...
And that about wraps up a top 10 most wanted for me.
There's still plenty more in the honourable mentions in the signature.