Since a thread finally reopened, gonna share my thoughts.
I am 100% sure, personally, that Geno is not getting in after the Mii costume being added, and with a Square character also being already present. Sure, there's no rule that two characters from the same company cannot be added in the same pass, but with the costume being added just two fighters ago...
However I am really curious how well Geno scored during the ballot. He did get a costume already in Smash 4, and was one of the four spirits allowed in the base game from Square Enix. Even Sakurai back in the day commented on the popularity of this character.
If Geno was to somehow happen, his only chance would be as a post-pass bonus. That's it. But he's always been a fascinating case for Smash where he marked the memories of so many people despite only appearing once.
Good luck. You guys deserve him.
God, I can't stay away! I see people being down about Geno's chances and it pulls me back in with the desire to give hope for my boi.
I CAN'T ESCAPE! SOMEONE GIVE ME A SEE YA! I NEED TO GET OUTTA HERE!
More importantly, Geno's costume doesn't mean anything towards his chances at all. This was a common misconception that basically all Geno fans (including myself and The Janitor) believed and we held on for dear life ever since MCW2. First and foremost, every single 3rd party costume is coming back: now we are only missing Lloyd, and his costume can come back with literally whoever they want, much like they already have for other costumes. Means nothing about his chances though, because as I mentioned before Pyra/Mythra we had 80%+ of the returning 3rd party costumes already and were only missing three, which is now down to one. It's clear that the intent to resell all the 3rd party costumes was there since the beginning of DLC development and thus wouldn't affect who was negotiated for and certainly won't in the future.
As for Square and their characters, it's silly to think that Sakurai or Nintendo would not get a character people wanted within their realm of possibility just because they already got another character from the same company. I will say that it has thus far been a pattern for it to not be as such, but with the number of big requests being slowly fulfilled it's not impossible to double dip that spicy Square chip, especially considering that Square arguably has the biggest library of character requests rivaled only by maybe Capcom. This is also a view that is limited with the mindset that Pass 2 is the end of DLC when we have many things that suggest otherwise, but I can't blame you for having the same mindset as most of the Smash community when they kinda force you to either samethink or it's wrongthink.
Last thing I will say is that ARMS and XBC2 both missed their chance at base because of Ultimate being in late development when these games were in early or mid-development. We got ARMS costumes, spirits and Spring Man AT and Rex costume and XBC2 spirits and music as a sort of consolation prize. Both of these series got a character and more content later on, and both of them were not the character we expected. However, not a single thing implies that Spring Man or Rex got passed over due to this prior content, in fact we have evidence that Spring Man is all about timing and Rex is simply design limitations. Had ARMS got a rep in base game, it likely would have been Spring Man, but the game was allowed to grow and the developers and fans to evolve, so instead Min Min was picked. Rex never had a chance since having that many character models of that detail was too much too handle, and you can't exclude either one of the girls, so Rex was the clear choice.
Thus, if Geno doesn't get in by the end of Ultimate's lifecycle (which is highly unlikely for a number of other reasons that I don;t have time to get into right now), it won't be because of a stupid Mii Costume: it would simply be because Square or Nintendo said no at the end of the day, or Sakurai and Co somehow couldn't make it happen, and I'm sure we all know the likelihood of these are very unprobable.
Though I find it interesting you mention post-pass bonus, as we have evidence one already existed for Pass 1. Geno isn't really a bonus choice unlike say Waluigi, so it's much more likely he either is one of the last two or he will be early in whatever way content continues for Smash Ultimate in the future.