First off, invented Hanafuda? I'd like to know where you got that piece of info, because it's not something I can find anywhere else. Producing Hanafuda cards is a very different thing from actually inventing them.
Hanafuda character
Chance: 10%
I certainly don't think it's impossible. You want to celebrate Nintendo history, then Hanafuda is a prime candidate bar none - without it, Nintendo might not exist at all. Having a major spot in Japan's general history of games as the one card game left relatively unharassed by a gambling-paranoid government, it's not something that can be brushed aside as simply a card game variant that made it big. It's not an unfeasible moveset either, especially when Mr. Game & Watch uses the same logic of cameoing its imagery as its moveset.
But I think it's also undeniable that the buck has always seemed to stop at electronic games. For such an important product, it's somehow failed to show up in any previous Smash game by any means or reference. Neither has the Ultra Hand, another product that uses no electronics despite being a very obvious choice for an item. The very furthest back that Smash goes seems to be the light gun, already represented by Duck Hunt - and even then, only through its NES appearances.
Sakurai doesn't owe anything to analog games, when we know it's specifically video games that caught his attention when he was young. The idea of a retro WTF is hardly a rule as much as it is a pattern, one with no promises behind it - just the director's desire to surprise us in every iteration. Something he already did when he declared that Everyone was Here.
Hanafuda would clearly be the next logical step in escalating the retro newcomers, of course - but that assumes that it has to keep ramping up! Yet if Smash must always pick an older, important representative, then where does it go after Hanafuda gets in, if Hanafuda's the absolute end of the line in regards to Nintendo history? Do we just assume Smash quietly dies and/or kills this rule only then? Or is it obliged to keep going even further back, digging into even older and more significant analog games? What comes next, four-suit deck for Smash? Backgammon for Smash? Gambling dice for Smash? Hanafuda itself would make just as little sense if not for its history with Nintendo! What I'm saying here is, you can't use "it must ramp up" as your main point of logic, because you'll simply reach absurdity right afterwards.
Alternatively, almost no one outside of Japan knows what Hanafuda is. Dozens of characters are written off over this. Takamaru and Lip always die for this. If you, a foreigner, asked Sakurai to put Hanafuda in, he might retort by asking you if you even knew what its rules were. I'd wager a good number of Japanese couldn't even answer that themselves.
What Hanafuda has, in spite of all this, is a century-long relationship with a Nintendo rivaled by nothing else, borne from its founder and continued by his great grandson, a man who chose to evolve Nintendo from a playing card company to the multi-billion dollar video game company it is today. Hanafuda wouldn't represent just the one surviving card deck that Nintendo adopted, it'd represent its whole pre-video game history. An undeniable legacy, to be certain - but as far as most the world is concerned, the history of Nintendo began with Donkey Kong, or Super Mario Bros. How far Sakurai himself sees Nintendo's history is all that would really decide Hanafuda's chances.
Want: 40%
I don't want to put Hanafuda in to satisfy some random "rule" that the internet vomited out just to justify G&W, R.O.B. and Duck Hunt to itself. I want them in because they represent a cool and obscure part of Nintendo history! What a thing to have your whole company be born from the game industry, especially when its other competitors can't claim the same! That's the kind of history lesson that any company would teach to the kids to make itself cooler.
Still, Ultimate is the most self-focused Smash yet, something that works way against Hanafuda's favor. Hanafuda wants a Nintendo-focused Smash to debut in, but Ultimate looks poised to invite the K. Rools and Shovel Knights instead of such callbacks. Frankly, there's just too many other choices that'll never have as good of a chance as getting in again, characters that'll certainly crowd the DLC line-up when it happens. Hanafuda has no such urgency behind it - its legacy and significance will remain the same for any future Smash game that might consider it, even if a roster reset or a remake happens.
Prediction:
Rowlet: 1%
Nominations:
Sans (boss) x5