AFAIK, Nintendouji has made no reference to specifically using Hanafuda cards, all that's been confirmed is it's "a turn-based card game with dungeon crawling RPG elements". When I first brought it up, I thought he would be the best way to use Hanafuda cards in a moveset, as he apparently uses cards to fight, and seems to be a reference to Nintendo itself, but, like I said, there has been no mention of what type of cards he uses as of yet, and personally I'm not expecting them to be Hanafuda cards. Of course, that doesn't mean he couldn't use them if ever implemented in Smash, I don't think it'd be that much of a stretch, but if he did, chances are it wouldn't be from his game. In fact, that's really the only way I see him ever being added, to sort of be an avatar for Hanafuda, not for the character himself (ofc if he starts getting more games, I guess things would be different).
By now IIRC his game is only a month away though, so there's not much more waiting time until we see what his game actually entails.