Aight let's get this in.
1. Phoenix Wright - He literally already has a moveset and his games have been published almost exclusively on Nintendo handhelds. Of course that's changing, but he's just as much of an icon as Simon Belmont in my eyes. While the AA series itself is rather niche, nearly everyone knows that memetic "OBJECTION" sound effect and speech bubble, so recognition is there.
2. Dante - While not really associated with Nintendo, he's appeared in Project X Zone, so that should count for something. Also you can say DMC isn't recognizable all you want, but that's even less true than it is for Ace Attorney.
3. Reimu - I could put Quote from Cave Story here, but I'm going with who I want, not who I expect. Also let's be honest here: Reimu has more of a chance than either Shovel Knight or Shantae simply due to the fact she's a Japanese character, and there's no western characters in Smash. At least, not yet. Plus, Touhou actually does have games on the Switch, so it's not even that farfetched.
4. Wonder Red - The Wonderful 101 was ****ing robbed. One of my favorite games of all time, honestly, yet it sold literally nothing because Nintendo barely marketed it. Hopefully when it gets ported to the Switch it'll sell more, and perhaps it'll even get a sequel.
5. Doomguy - If Bethesda HAS to have a rep in Smash, it's gotta be Doomguy. Doomguy's weapons are less realistic in Quake Champions, so Sakurai could just use those. Also, not only was the Switch port of NuDoom heavily promoted, but Doom has a game exclusive to Nintendo consoles: Doom 64.