For Gameplay stuff
-I Want a Character that Fights by Glitching out the Game, which is Something I haven't seen Done before in any Game. I think Missingno would fit Very well, and would make a Good Surprise Character in Smash 6
-I want a Character that Has Portals As a Gimmick. So Someone like Chell from Portal, Wraith from Apex Legends, and Noob Saibot from Mortal Kombat would be good. Speaking of Noob
-I want a Character that Fights using a Clone. Noob would be amazing for this, But I actually think if they Make Dark Samus Unique, they could give her Clone ability to her in Smash 6
-I want a Character with Permanent Transformations, or Transformations you can Stay in forever if you keep up your Resources. I want Goku to have this, but Agumon would also work well
-I Want a Character with a Katana and Iado Fight style, and I want Vergil to take that mantle, but I also Really don't mind and Would be Cool with Lyn. In fact I wouldn't mind if we got her this FP2 (and would be kinda Excited) even if she be 9th Fire Emblem Character, but she deserves it though
-I want a Character that, as one of my friends said it "Rewards you for Doing Good" Pretty much you get buffed for Playing well, pretty much the Opposite of Lucario's Aura Mechanic. I think Dante (and Vergil) would make use of this well with the Style Ranking. Perhaps the more Style you have the better Damage you do, or Perhaps the longer you Devil Trigger lasts
-I Want a Character that Manipulates Time and Space, but in a More Offensive manner, like Dio's Time Freeze or Geras Time Moves, or maybe even Sakuya Izayoi Time shenigains with her Knives. But Of Course I want SHADOW THE HEDGEHOG to do this among all else. Bayonetta witch Time isn't as cool since it's a Counter
-I want a Character that has Teleport Combos or Teleport Cancels like DBZ. Goku and Shadow would Be perfect for this. I know there's the Ledge cancel thing but I want to do these without the Need for Ledges
-I want a Character with an Airdash. Reimu could probably have this, or perhaps Sol badguy or Ragna, but I'd prefer Reimu
-I want More characters with Super Armor, like Little Mac, especially if they re-tune Make in Smash 6 and take away his Super Armor. I think Black Knight would be Cool, but My Dream pick would be Broly.
I Want a Character with a Scythe, and I also want Characters with Lightsabers or Beam Swords (Shulk's Beam sword does not have Lightsaber sound effects). Travis would be good for later, but besides Zasameal from Soul Calbur, I can't think of anyone else
I Want a Character that fights using Dancing, like if they put Michael Jackson in Smash. Waluigi Unironically would be good for this, since his Most Important role was in Mario Dance Dance Revolution
Just.... Why? Like, even if by some miracle Shadow is in Bayonetta 3, why would he be chosen to promote that game? That would be the same thing as Nintendo choosing Dante to promote Shin Megami Tensei 3 HD. If they want to promote Bayonetta 3 that bad they would just go with Jeanne, Balder or Rodin.
Here's the Thing
Bayonetta 3 wouldn't be the Sole reason Shadow gets in, but it could be major factor in him getting chosen over Other Characters.
People want Shadow, and People, even Casuals, know who Shadow is. If Shadow was in Bayonetta 3, that would get more people interested. If Shadow was in Smash, that would also give more attention towards Bayonetta 3 in the Process.
Much More People want and Know who Shadow is than Jeanne, Balder, and Rodin.
Nintendo might have even asked Sega, and then Platinum if they could add Shadow to the Game, Since Sonic Is still selling very well, especially on Nintendo (with Forces and Mania Especially), and Sonic been killing it on Mobile. Shadow fits The Bayonetta universe very well so It's like Win Win