NDA prevent people from talking about anything concerning(in Smash case) the character in question and Super Smash Bros. Ultimate. The NDA is to allow Nintendo themselves to announce said character(s).
I do not have any doubts whatsoever. It's just people do not understand that you can't explain the radio silence when it comes to Shantae and Smash Bros Ultimate can be explain in only one way, an NDA. Like it was stated above by you "If Shantae isn't in Ultimate in ANY shape or form then they would not need to hide that fact from their loyal fans"(aka US). Same goes with the excuse of a "Shantae Fighting Game" because they would not be under a NDA and could once again state she isn't in Smash and kill the hype before it even starts.
The way WayForward is handling this is weird in general(unless an NDA is involved and even then it would not prevent Shantae to be in Blade Strangers if Shantae was just an Assist Trophy in Ultimate).
Word.
We can be confident about Shantae being in Smash, for this.
Of course, whether or not she will be a fighter, remains to be seen.
Assist Trophy would be a bummer, but at least she'd be in the game and it'd still benefit her.
But yeah, it seems that at this point, some people want to keep their hopes down so forcefully, that they resort to random, made-up things, to deconfirm her.
The above point still stands strong though. And it's easily one of the strongest clues, for her being in Smash.
And speaking of Assist Trophies, I just remembered that there is another thing I wanted to talk about.
Assist Trophies won't be made into playable characters later!
Seriously, Waluigi fans are still in denial and cling onto that hope.
But I am afraid it won't come to pass.
And if Shantae is revealed as an Assist Trophy, just accept it and take solace that she's still in the game and benefits from the exposure she's getting.
And please...
STOP seeing Assist Trophies as mockeries or insults. That's NOT what they are supposed to be!
Like I said before, Sakurai didn't create Assist Trophies to mock characters.
Far from it, he still sees them as valuable.
It's his way to give characters some much needed representation and love, outside of just being a fighter.
And in cases like "Shovel Knight" or "Bomberman" it's very likely that he couldn't realize them as fighters.
But instead of throwing them out of the game entirely, he still decided to give them representation, as a summon.
Assist Trophies are not the bottom of the barrel, they're a close second to being a fighter.
And it's for that reason, that it's extremely unlikely for Assist Trophies to become playable characters later.
Not only would it be backpedaling, they would also have to remove content and rework some parts of it, which surely is a lot harder than many people think...
Honestly, if Sakurai can see a character as a playable fighter, I'm sure he would've made said character a fighter in the first place.
Making an Assist Trophy, only to remove it later and rework it to be a playable character, seems like much more trouble to me, than it's worth.
The reason people think so lowly of Assist Trophies, is just because they're being greedy.
Whatever characters they hold dear, they will only accept as playable fighter.
Anything less, they get salty.
And for the love of God:
Don't hold WayForward responsible for this and start boycotting them.
Whatever role Shantae will have in Smash, is up to Sakurai and his team. It's completely out of WayForward's control!