1: She's a Spirit. Spirits 100% deconfirm and I've believed that since day 1. For more info on that, please look at the last part of
this thread's original post.
2: No NDAs. WF and Shantae's Voice Actress both talked about Shantae in Smash, which would break a Non Disclosure Agreement.
3: She's the Who of Spirits? Shantae appeared a lot in the promotional content for Spirits. Due to her being highly requested, it makes sense to do this to sell sprits mode as a whole. Sound familiar? It should, because Waluigi is treated the same way for Assist Trophies. Shantae's the Waluigi of Assist Trophies, and we're all well aware Waluigi will NEVER be in Smash.
4: On the spectrum of Nindies, there are many characters to choose from. So why Shantae when her competition has so much else going for them with Nintendo and gaming as a whole? Shovel Knight was important enough to be given a better role than Shantae (even though it deconfirms him, too). Suda51, who is behind No More Heroes, is friends with Sakurai, meaning Travis has a better shot than her. There's also Commander Video, who was a Trophy before Shantae was even talked about. Additionally, Reimu from Touhou is a Japanese icon, Frisk and sans are icons worldwide. What does Shantae have that can stand up to them? Cadence was able to get a crossover with an OFFICIAL NINTENDO PROPERTY. not just any IP, but Zelda! Last but certainly not least, Steve is from the best-selling game of all time. With so many of these characters with great merits in their corner, with some of them being way more popular than Shantae, how is she supposed to stand a chance against any one of them, let alone every one of them?
5: An actually new one. She's unknown in Japan. The only reason people are starting to har of Shantae over there is because of the collaboration with Trigger. Before then, when Smash DLC was actually decided,
6: She's extremely obscure in general. How many of you heard of Shantae before smash speculation, let alone actually played her games? Not many.
7: She has a huge hate base. Everywhere you look, you will find Shantae detractors. Whether they simply don't like the character, have another indie rep that they'd rather see over her, people who think that Shantae fans want her for reasons im not sure i can say without getting banned, and people who just hate her for the sake of hating her. Compare that to the amount of Shantae fans, and you've got an already anti-Shantae board looking even worse for the Half-Genie Zero.
8: Where is her spirit found? In World of Light. Do you know how much of a headache it would be for the Smash team to handle one of those spirits specifically? Let's assume she did beat the impossible odds. First, they have to make the actual fighter, which is already a huge toll on the team. Then they have to find what they have to do with that little png file on the bridge. Then they have to find a way to allow players to still be able to access her spirit battle while letting you play as her in WOL. Then they need to write a whole lore-wise explanation for how someone who was prominently killed in Galeem's attack, yet has a body and is able to help Kirby. It's either that or pick another fighter.
9: Other fighters would make more money. Nintendo's a business. They want money. Who would make Nintendo the least money? A triple A juggernaut? A breakout indie star who's become a big household name in so little time, or Shantae?
10: Why would Sakurai pick her? As far as we know, Sakurai only knows of her as "that one character in North America people keep annoying me about". This is basically my catch-all argument, because Sakurai and/or Nintendo could have reasons for not picking her to be a fighter that we wouldn't even guess unless we were told from reliable sources.
Counterarguments:
"Spirits don't deconfirm": please look at the last part of
this thread's original post.
"But the window/other evidence!": How do we know if that's even intentional. Let's assume it was intentional. It is probably a fake teaser to stir up hype for her. They already did it before, with the last DLC for HGH having a Smash crossover (ie Smash x Castlevania) reference in the trailer, and an "Everyone is Here" reference in Jammies mode. That amounted to nothing. After breaking NDA, they can't turn around and tease her again with her actually being in.
It's pretty plain to see that Shantae doesn't stand a chance to get into Smash, and again, I actually unironically believe that she's one of the few characters to be
less likely than Shrek and Goku. She has that much stacked against her.